[Minor] Crumbling FOFs can crumble twice

Ok this is REALLY minor, but crumbling FOFs (for example, linedef type 123 - Crumbling, Respawn, Floating, Bobbing - the one I tested this on) can 'crumble' twice if you jump onto them and immediately do a short hop so that you land on the platform a second time before they crumble.

(Notice the second * [Crumbling] sound caption.)

Respawning ones (again, such as 123) will flicker a bit weirder than usual and respawn twice (the first time they'll fall again, the second they'll stay) if this happens.

Recorded on 2.2.10 RC1. Not sure if this happens in 2.2.9.