blocking or unblocking levitation or flight

blocking or unblocking levitation or flight

when level teleporting or digging.  Level teleporting while levitation
was blocked due to being inside solid rock didn't notice that it should
be unblocked until you moved from whatever type of terrain you landed
on (room, for instance) to some other type (such as corridor).  Digging
down to make a pit or hole while inside solid rock converts that spot
to floor so should also check whether to unblock levitation/flying, and
not fall if unblocking occurs.