Run uploadVideo on main thread

Riot/Modules/Room/RoomViewController.m

@@ -8095,7 +8095,9 @@ static CGSize kThreadListBarButtonItemImageSize;
                     // First make a copy of the video in the temp directory because the video at videoURL
                     // is a copy by the iOS photo picker and will be dismissed when this completion block ends
                     NSURL *videoCopy = [self makeVideoCopy:videoURL];
-                    [self uploadVideo:videoCopy];
+                    dispatch_async(dispatch_get_main_queue(), ^{
+                        [self uploadVideo:videoCopy];
+                    });
                 }
             }];
         }