qt/MLVideoModel: don't reset model on media update event

when you're browsing medialibrary (video view) and stop a playing video, it causes the video view to be reset this MR fixes it

only update changed item instead of resetting whole model

also only reset model if added item is a video

modules/gui/qt/medialibrary/mlvideomodel.cpp

@@ -147,6 +147,8 @@ void MLVideoModel::onVlcMlEvent(const MLEvent &event)
     switch (event.i_type)
     {
         case VLC_ML_EVENT_MEDIA_ADDED:
+            m_need_reset = (event.creation.media.i_type == VLC_ML_MEDIA_TYPE_VIDEO);
+            break;
         case VLC_ML_EVENT_MEDIA_DELETED:
             m_need_reset = true;
             break;