Bail out of trap-disarming at diff 99

Basically, if it's impossible to disarm the trap, tell the player as
much and return, rather than splashing lava, sticking your head in the
pit, etc.

Fixes #7757.
Merge pull request #7964 from KA101/NoDisarm

(Blocker-Fix) Bail out of trap-disarming at diff 99