Rare render bugs

[Pyrdacor]

This is a collective issue for several spotted rendering bugs. Some bugs might be already fixed.

To work on them:

1. Try to reproduce
2. Try to track down the behavior by code observation and logical considerations
3. Debug and fix them if possible
4. Remove them if not reproducable

Seen rendering bugs:

• Stonecutter building with the burning flames behind it
• Sometimes a serf is drawn that is inside the castle (leaving the castle)
• Sometimes borders remain from the last game (not deleted properly?)