Fix mypy daemon crash when following from a new module (#10030)

File watcher state for files added to the build wasn't updated
correctly, resulting in crashes.

I couldn't find a way to reproduce this in our test environment,
so I only tested this manually.

Fixes #10029.

mypy/dmypy_server.py

@@ -620,12 +620,12 @@ def refresh_file(module: str, path: str) -> List[str]:
 
         fix_module_deps(graph)
 
-        # Store current file state as side effect
-        self.fswatcher.find_changed()
-
         self.previous_sources = find_all_sources_in_build(graph)
         self.update_sources(self.previous_sources)
 
+        # Store current file state as side effect
+        self.fswatcher.find_changed()
+
         t5 = time.time()
 
         manager.log("fine-grained increment: update: {:.3f}s".format(t5 - t1))