Open doors can be constructed over
Describe the bug
You can currently build window frames, door frames, floors, walls and stairs etc in open doors which makes the original door and it's frame effectively disappear. You can't build any of these in empty door frames.
For multi tile gates/doors this unsurprisingly cuts the gate in two when closed

This is caused by the FLAT flag which is what construction's check_empty checks against, removing the flag isn't a clean fix though bc that's also used to determine what you can drag furniture into among other things
Attach save file
N/A
Steps to reproduce
- Find a door and open it
- Construct a wooden staircase in the same tile
- Behold as your character obliges
Expected behavior
Open doors shouldn't be able to be constructed over
Screenshots
No response
Versions and configuration
- OS: Windows 10
- Game Version: 0.G-923-g6d311a79b1
- Graphics Version: Tiles
- In-game Language: English
- Mods Loaded: Default
Additional context
No response
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/confirm