Center only on display 1. No more multimonitor span.

src/sdl/i_video.c

@@ -198,13 +198,13 @@ static void SDLSetMode(INT32 width, INT32 height, SDL_bool fullscreen)
 			glfallbackresolution = SDL_FALSE;
 			SDL_SetWindowFullscreen(window, 0);
 			SDL_SetWindowSize(window, width, height);
-			SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
+			SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED_DISPLAY(1), SDL_WINDOWPOS_CENTERED_DISPLAY(1));
 		}
 		else if (!wasfullscreen)
 		{
 			// Reposition window only in windowed mode
 			SDL_SetWindowSize(window, width, height);
-			SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
+			SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED_DISPLAY(1), SDL_WINDOWPOS_CENTERED_DISPLAY(1));
 		}
 	}
 	else