engraving with empty wand

From a bug report:  if you
attempted to engrave with an empty wand while levitating, it wouldn't use
a turn unless you successfully wrested an extra charge out of the wand.
So you could always get such charge in a single elapsed turn of game time
if you didn't care about zapping in any particular direction; extremely
useful for wishing.

     Noticed when checking this:  when you did wrest the extra charge,
the engraving code accessed freed memory for the wand after it had been
used up.

     Lastly, wands producing certain effects always become discovered,
even when you don't yet know what they look like.  (This part of the patch
is trunk-only since it utilizes the routine which fixes similar case for
zapping.)

doc/fixes34.4

@@ -297,6 +297,9 @@ can't throw if poly'd into form which lacks hands
 can't eat an artifact you're unable to touch
 attempting to kick beyond map edge performed an out of array bounds memory
 	access; symptom seen was "show_glyph: bad pos" warning when blind
+attempting to engrave with an empty wand should use a turn even when hero is
+	levitating--trying and failing to wrest a charge takes time
+don't access freed memory after engraving "wrests one last charnge" from wand
 
 
 Platform- and/or Interface-Specific Fixes