R759 - delayed were change could cause crash

moveloop() sets a flag when a were/poly change should occur, but it
delays this change if the hero is Unchanging or cannot be interrupted (e.g.
praying).  However, by the time the change can be applied, the reason
may no longer be valid.  Reset the change indicator when this is the case.
Avoids possible strange polymorphs and were crashes.

doc/fixes34.1

@@ -53,6 +53,7 @@ avoid temporary disappearing Burdened message due to updating status line
 don't credit player's wisdom when makelevel creates random Elbereth engravings
 reduce insect/monster creation from monster spells
 avoid "couldn't place lregion type 5" warning when arriving at Plane of Fire
+avoid crash due to delayed poly or were change no longer being valid
 
 
 Platform- and/or Interface-Specific Fixes

src/allmain.c

@@ -233,6 +233,10 @@ moveloop()
 			    }
 #endif
 			}
+			/* delayed change may not be valid anymore */
+			if ((change == 1 && !Polymorph) ||
+			    (change == 2 && u.ulycn == NON_PM))
+			    change = 0;
 			if(Polymorph && !rn2(100))
 			    change = 1;
 			else if (u.ulycn >= LOW_PM && !rn2(80 - (20 * night())))