Fix meat gibs from skeletons

Fixes #8489 - code had meat gibs as default (when the monster was not an insect or similar). Now skeletons will simply not create any gibs.

Also fixes placing chunks of meat behind a wall. To reproduce: place a small (meat based) critter in the south-west corner of the evac shelter, get a shotgun and kill the critter with it. This will create meat chunks (and blood) all over the place. Some meat chunk items are placed *on* the surrounding walls (which do not allow items on them). The map class automatically moves those items to the nearest square that allows items, which happens to be outside (the other side of the wall).