Store window size on size change event.

Allows arbitrary sized windows on Darwin... the OS is still scaling
the window contents though rather than allowing us to dynamically
update them.

src/conio/sdl_con.c

@@ -460,8 +460,11 @@ static void internal_setwinsize(struct video_stats *vs, bool force)
 		pthread_mutex_lock(&win_mutex);
 		sdl.GetWindowSizeInPixels(win, &w, &h);
 		pthread_mutex_unlock(&win_mutex);
-		if (w != vs->winwidth || h != vs->winheight)
+		if (w != vs->winwidth || h != vs->winheight) {
+			vs->winwidth = w;
+			vs->winheight = h;
 			changed = true;
+		}
 		pthread_mutex_unlock(&vstatlock);
 		vstat.scaling = sdl_getscaling();
 	}