Do not create empty overlays with the evaporate property (Bug#9642).

Do not create empty overlays with the evaporate property (Bug#9642).

* buffer.c (Fmove_overlay): Delete an evaporating overlay
if it becomes empty after its bounds are adjusted to fit within
its buffer.  Without this fix, in a nonempty buffer (let ((o
(make-overlay 1 2))) (overlay-put o 'evaporate t) (move-overlay o 0 1))
yields an empty overlay that has the evaporate property, which is
not supposed to happen.