[ui] app: Don't read QSettings again when updating thumbnails for pro…

…jects

There is no need to read the QSettings again as the content of
`self._recentProjectFiles` reflects their content accurately and they
do not store any thumbnail-related information.

QSettings will now only be read once, upon Meshroom's start.

meshroom/ui/app.py

@@ -413,9 +413,14 @@ def updateRecentProjectFilesThumbnails(self) -> None:
         available.
         """
         if not self._updatedRecentProjectFilesThumbnails:
-            self._recentProjectFiles = self._getRecentProjectFiles()
+            self._updateRecentProjectFilesThumbnails()
             self._updatedRecentProjectFilesThumbnails = True
 
+    def _updateRecentProjectFilesThumbnails(self) -> None:
+        for project in self._recentProjectFiles:
+            path = project["path"]
+            project["thumbnail"] = self._retrieveThumbnailPath(path)
+
     @Slot(str)
     @Slot(QUrl)
     def addRecentProjectFile(self, projectFile) -> None: