Merge image flags from config and label file

labelme/app.py

@@ -1317,12 +1317,12 @@ class MainWindow(QtWidgets.QMainWindow):
         if self._config['keep_prev']:
             prev_shapes = self.canvas.shapes
         self.canvas.loadPixmap(QtGui.QPixmap.fromImage(image))
-        if self._config['flags']:
-            self.loadFlags({k: False for k in self._config['flags']})
+        flags = {k: False for k in self._config['flags'] or []}
         if self.labelFile:
             self.loadLabels(self.labelFile.shapes)
             if self.labelFile.flags is not None:
-                self.loadFlags(self.labelFile.flags)
+                flags.update(self.labelFile.flags)
+        self.loadFlags(flags)
         if self._config['keep_prev'] and not self.labelList.shapes:
             self.loadShapes(prev_shapes, replace=False)
             self.setDirty()