macosx: fixed crash when setting up the video output

AppKit could be accessed by a non-main-thread

This is a manual backport of 9dd2f6ed46b8c4bb0399693dbb3f91d7efbfabb0

modules/gui/macosx/MainWindow.h

@@ -175,7 +175,7 @@
 - (void)drawFancyGradientEffectForTimeSlider;
 
 - (id)videoView;
-- (id)setupVideoView;
+- (void)setupVideoView;
 - (void)setVideoplayEnabled;
 - (void)resizeWindow;
 - (void)setNativeVideoSize:(NSSize)size;

modules/gui/macosx/MainWindow.m

@@ -1568,7 +1568,7 @@ static VLCMainWindow *_o_sharedInstance = nil;
     return o_video_view;
 }
 
-- (id)setupVideoView
+- (void)setupVideoView
 {
     vout_thread_t *p_vout = getVout();
     if ((var_InheritBool( VLCIntf, "embedded-video" ) || b_nativeFullscreenMode) && b_video_deco)
@@ -1619,7 +1619,6 @@ static VLCMainWindow *_o_sharedInstance = nil;
             [[o_video_view window] setLevel: NSNormalWindowLevel];
         vlc_object_release( p_vout );
     }
-    return o_video_view;
 }
 
 - (void)setVideoplayEnabled

modules/gui/macosx/intf.m

@@ -1769,7 +1769,8 @@ unsigned int CocoaKeyToVLC( unichar i_key )
 
 - (id)getVideoViewAtPositionX: (int *)pi_x Y: (int *)pi_y withWidth: (unsigned int*)pi_width andHeight: (unsigned int*)pi_height
 {
-    id videoView = [o_mainwindow setupVideoView];
+    [o_mainwindow performSelectorOnMainThread:@selector(setupVideoView) withObject:nil waitUntilDone:YES];
+    id videoView = [o_mainwindow videoView];
     NSRect videoRect = [videoView frame];
     int i_x = (int)videoRect.origin.x;
     int i_y = (int)videoRect.origin.y;