macosx: fix main menu initialization order on startup

MainMenus p_intf can be already accessed before
applicationWillFinishLaunching was called.

This should fix quite some crashes reported by the users.

modules/gui/macosx/MainMenu.m

@@ -139,12 +139,12 @@ static VLCMainMenu *_o_sharedInstance = nil;
     }
 
     [self setRateControlsEnabled:NO];
+
+    p_intf = VLCIntf;
 }
 
 - (void)applicationWillFinishLaunching:(NSNotification *)o_notification
 {
-    p_intf = VLCIntf;
-
     NSString* o_key;
     playlist_t *p_playlist;
     vlc_value_t val;