Fix text getting appended to vid_restart in command buffer

I was getting unknown command "vid_restart-button2" warning on OSX when trying to use alt-return to toggle fullscreen.

code/sdl/sdl_glimp.c

@@ -808,7 +808,7 @@ void GLimp_EndFrame( void )
 		{
 			// SDL_WM_ToggleFullScreen didn't work, so do it the slow way
 			if( !sdlToggled )
-				ri.Cmd_ExecuteText(EXEC_APPEND, "vid_restart");
+				ri.Cmd_ExecuteText(EXEC_APPEND, "vid_restart\n");
 
 			ri.IN_Restart( );
 		}