Fix #8784: using alt+enter didn't update the fullscreen toggle visibly (#8820)

Basically, the window was not invalidated, so it was never redrawn.
This made it look like it wasn't working, but it really was.

src/video/cocoa/cocoa_v.mm

@@ -201,6 +201,7 @@ bool VideoDriver_Cocoa::ToggleFullscreen(bool full_screen)
 		[ NSMenu setMenuBarVisible:!full_screen ];
 
 		this->UpdateVideoModes();
+		InvalidateWindowClassesData(WC_GAME_OPTIONS, 3);
 		return true;
 	}