Fix switching to software

Would show a black screen for me on Linux. My suspsicion is that
some things are not initialized with just VID_CheckRenderer.

src/screen.c

@@ -203,6 +203,8 @@ void SCR_SetMode(void)
 		needpatchflush = true;
 		needpatchrecache = true;
 		VID_CheckRenderer();
+		if (!setmodeneeded)
+			VID_SetMode(vid.modenum);
 	}
 
 	if (setmodeneeded)