only override buffer when the world is ready

This fixes drawing UI to the title screen (e.g. the Generic Mod Config Menu button).

Author: Pathoschild

src/SMAPI/Framework/SGame.cs

@@ -157,8 +157,10 @@ public override bool ShouldDrawOnBuffer()
         //
         // It's not clear why that happens, but there's little reason not to just using the buffer consistently and
         // avoid the issue.
+        if (Context.IsWorldReady)
+            return true;
 
-        return true;
+        return base.ShouldDrawOnBuffer();
     }
 
     /*********