Wand of digging in a shop crash

From a bug report.  I haven't looked closely, but I think this bug is just
in the development code.  If you dig in a shop with a wand while carrying
unpaid stuff, the shopkeeper would grab your pack, including the wand but
w/o clearing current_wand.  It seems the right thing is to just not grab
the current_wand, since it's not in your pack while you're zapping it.
In 3.4.0, you lost the wand too.

src/shk.c

@@ -3377,6 +3377,7 @@ register int fall;
 		if ((obj->owornmask & ~(W_SWAPWEP|W_QUIVER)) != 0 ||
 			(obj == uswapwep && u.twoweap) ||
 			(obj->otyp == LEASH && obj->leashmon)) continue;
+		if (obj == current_wand) continue;
 		setnotworn(obj);
 		freeinv(obj);
 		subfrombill(obj, shkp);