macosx: when main window is hidden, let playlist menu item only display the window

Furthermore, this commit fixes close button functionality in dark ui style when video is playing
(cherry picked from commit 2709f26e)
Signed-off-by: David Fuhrmann <david.fuhrmann@googlemail.com>

modules/gui/macosx/MainWindow.m

@@ -634,9 +634,10 @@ static VLCMainWindow *_o_sharedInstance = nil;
 
 - (IBAction)togglePlaylist:(id)sender
 {
-    if (![self isVisible])
+    if (![self isVisible] && sender != nil)
     {
         [self makeKeyAndOrderFront: sender];
+        return;
     }
 
     BOOL b_activeVideo = [[VLCMain sharedInstance] activeVideoPlayback];