Combine ways silently combines when tag is not present on one way but present on the other

[AM909]

If you have a way with layer=1 and another way with no layer tag, and you combine them, the conflict dialog comes up but just says "no conflicts". The new way will have layer=1, which may be incorrect.

I can't think of any cases where it should do this. There are probably some "who cares" cases (like created_by), but it's still not technically correct.