Library Scanner: sort files before adding

Sort files in each scanned directory alphabetically before adding.
This causes folders which contain track numbered files to be added
in it's natural order, so sorting after date added also sorts for track
numbers. Since the tracks will have slightly different timestamps, using a
second sorting does not work.

src/library/scanner/recursivescandirectorytask.cpp

@@ -1,7 +1,8 @@
 #include "library/scanner/recursivescandirectorytask.h"
 
 #include <QCryptographicHash>
-#include <QDirIterator>
+#include <QDir>
+#include <QFileInfo>
 
 #include "library/scanner/importfilestask.h"
 #include "library/scanner/libraryscanner.h"
@@ -34,8 +35,10 @@ void RecursiveScanDirectoryTask::run() {
     // Filter from the QDir so we have to set it first. If the QDir has not done
     // any FS operations yet then this should be lightweight.
     auto dir = m_dirAccess.info().toQDir();
-    dir.setFilter(QDir::Dirs | QDir::Files | QDir::NoDotAndDotDot);
-    QDirIterator it(dir);
+    dir.setFilter(QDir::Dirs | QDir::Files | QDir::NoDotAndDotDot | QDir::System);
+    // sort directory by file name to increase chance that files are sorted sensible
+    dir.setSorting(QDir::SortFlag::DirsFirst | QDir::SortFlag::Name);
+    QFileInfoList children = dir.entryInfoList();
 
     std::list<QFileInfo> filesToImport;
     std::list<QFileInfo> possibleCovers;
@@ -50,9 +53,9 @@ void RecursiveScanDirectoryTask::run() {
     QRegularExpression supportedCoverExtensionsRegex =
             m_scannerGlobal->supportedCoverExtensionsRegex();
 
-    while (it.hasNext()) {
-        QString currentFile = it.next();
-        QFileInfo currentFileInfo = it.fileInfo();
+    for (auto it = children.begin(); it != children.end(); ++it) {
+        QFileInfo currentFileInfo = *it;
+        QString currentFile = currentFileInfo.filePath();
 
         if (currentFileInfo.isFile()) {
             const QString& fileName = currentFileInfo.fileName();