Catch and ignore UniqueConstraintViolationException in file cache insert

* caused by a concurrect insert that happens between the INSERT and it's sub-SELECT which was there to actually avoid it within insertIfNotExists - sub selects are not atomic and allow this
* see also #12315

Avoids an error that has this stack trace:

```
Doctrine\DBAL\Exception\UniqueConstraintViolationException: An exception occurred while executing 'INSERT INTO "oc_filecache" ("mimepart","mimetype","mtime","size","etag","storage_mtime","permissions","checksum","path_hash","path","parent","name","storage") SELECT ?,?,?,?,?,?,?,?,?,?,?,?,? FROM "oc_filecache" WHERE "storage" = ? AND "path_hash" = ? HAVING COUNT(*) = 0' with params [1, 2, 1502911047, -1, "59949a47cabae", 1502911047, 31, "", "fb66dca5f27af6f15c1d1d81e6f8d28b", "files_trashbin", 1742774, "files_trashbin", 136, 136, "fb66dca5f27af6f15c1d1d81e6f8d28b"]:

SQLSTATE[23505]: Unique violation: 7 ERROR: duplicate key value violates unique constraint "fs_storage_path_hash"
DETAIL: Key (storage, path_hash)=(136, fb66dca5f27af6f15c1d1d81e6f8d28b) already exists.

3rdparty/doctrine/dbal/lib/Doctrine/DBAL/DBALException.php - line 128: Doctrine\DBAL\Driver\AbstractPostgreSQLDriver->convertException('An exception oc...', Object(Doctrine\DBAL\Driver\PDOException))
3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php - line 1015: Doctrine\DBAL\DBALException driverExceptionDuringQuery(Object(Doctrine\DBAL\Driver\PDOPgSql\Driver), Object(Doctrine\DBAL\Driver\PDOException), 'INSERT INTO "oc...', Array)
lib/private/DB/Connection.php - line 213: Doctrine\DBAL\Connection->executeUpdate('INSERT INTO "oc...', Array, Array)
lib/private/DB/Adapter.php - line 114: OC\DB\Connection->executeUpdate('INSERT INTO "oc...', Array)
lib/private/DB/Connection.php - line 251: OC\DB\Adapter->insertIfNotExist('*PREFIX*filecac...', Array, Array)
lib/private/Files/Cache/Cache.php - line 273: OC\DB\Connection->insertIfNotExist('*PREFIX*filecac...', Array, Array)
lib/private/Files/Cache/Cache.php - line 230: OC\Files\Cache\Cache->insert('files_trashbin', Array)
lib/private/Files/Cache/Scanner.php - line 279: OC\Files\Cache\Cache->put('files_trashbin', Array)
lib/private/Files/Cache/Scanner.php - line 216: OC\Files\Cache\Scanner->addToCache('files_trashbin', Array, -1)
lib/private/Files/Cache/Scanner.php - line 175: OC\Files\Cache\Scanner->scanFile('files_trashbin')
lib/private/Files/Cache/Scanner.php - line 322: OC\Files\Cache\Scanner->scanFile('files_trashbin/...', 3, -1, NULL, false)
lib/private/Files/Cache/Updater.php - line 124: OC\Files\Cache\Scanner->scan('files_trashbin/...', false, 3, false)
lib/private/Files/View.php - line 321: OC\Files\Cache\Updater->update('files_trashbin/...', 1502911047)
lib/private/Files/View.php - line 1151: OC\Files\View->writeUpdate(Object(OCA\Files_Trashbin\Storage), 'files_trashbin/...')
lib/private/Files/View.php - line 269: OC\Files\View->basicOperation('mkdir', '/files_trashbin...', Array)
apps/files_trashbin/lib/Trashbin.php - line 154: OC\Files\View->mkdir('files_trashbin/...')
apps/files_trashbin/lib/Trashbin.php - line 225: OCA\Files_Trashbin\Trashbin setUpTrash('klas')
apps/files_trashbin/lib/Storage.php - line 247: OCA\Files_Trashbin\Trashbin move2trash('Photos', false)
apps/files_trashbin/lib/Storage.php - line 189: OCA\Files_Trashbin\Storage->doDelete('files/Photos', 'rmdir')
lib/private/Files/View.php - line 1136: OCA\Files_Trashbin\Storage->rmdir('files/Photos')
lib/private/Files/View.php - line 348: OC\Files\View->basicOperation('rmdir', '/Photos', Array)
apps/dav/lib/Connector/Sabre/Directory.php - line 303: OC\Files\View->rmdir('/Photos')
3rdparty/sabre/dav/lib/DAV/Tree.php - line 179: OCA\DAV\Connector\Sabre\Directory->delete()
3rdparty/sabre/dav/lib/DAV/CorePlugin.php - line 287: Sabre\DAV\Tree->delete('Photos')
[internal function] Sabre\DAV\CorePlugin->httpDelete(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
3rdparty/sabre/event/lib/EventEmitterTrait.php - line 105: call_user_func_array(Array, Array)
3rdparty/sabre/dav/lib/DAV/Server.php - line 479: Sabre\Event\EventEmitter->emit('method DELETE', Array)
3rdparty/sabre/dav/lib/DAV/Server.php - line 254: Sabre\DAV\Server->invokeMethod(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
apps/dav/appinfo/v1/webdav.php - line 71: Sabre\DAV\Server->exec()
remote.php - line 162: require_once('/var/www/nextcl...')
{main}
```

Signed-off-by: Morris Jobke <[email protected]>

lib/private/Files/Cache/Cache.php

@@ -37,6 +37,7 @@
 
 namespace OC\Files\Cache;
 
+use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use Doctrine\DBAL\Driver\Statement;
 use OCP\Files\Cache\ICache;
@@ -268,12 +269,19 @@ public function insert($file, array $data) {
 			return trim($item, "`");
 		}, $queryParts);
 		$values = array_combine($queryParts, $params);
-		if (\OC::$server->getDatabaseConnection()->insertIfNotExist('*PREFIX*filecache', $values, [
-			'storage',
-			'path_hash',
-		])
-		) {
-			return (int)$this->connection->lastInsertId('*PREFIX*filecache');
+		try {
+			if (\OC::$server->getDatabaseConnection()->insertIfNotExist('*PREFIX*filecache', $values, [
+				'storage',
+				'path_hash',
+			])
+			) {
+				return (int)$this->connection->lastInsertId('*PREFIX*filecache');
+			}
+		} catch (UniqueConstraintViolationException $e) {
+			// if this is thrown then a concurrent insert happened between the insert and the sub-select in the insert, that should have avoided it
+			// it's fine to ignore this then
+			//
+			// more discussions about this can be found at https://github.com/nextcloud/server/pull/12315
 		}
 
 		// The file was created in the mean time