Fix: Possible crash when saving bones after second death

ukiller was not cleared when life-saved, so if you went on to some other level and died again in a way that didn't overwrite ukiller (e.g. a wand zap), then savebones() would encounter the dangling pointer.

Author: saltwaterterrapin

doc/evilhack-changelog.md

@@ -3600,4 +3600,5 @@ The following changes to date are:
   various objects
 - Fix: feedback when having to drop a worn shield vs worn bracers
 - Fix: Tortle archeologists could never throw Xiuhcoatl
+- Fix: Possible crash when saving bones after second death
 

src/end.c

@@ -1033,6 +1033,8 @@ int how;
 {
     int uhpmin;
 
+    ukiller = (struct monst *) 0;
+
     /* life-drain/level-loss to experience level 0 kills without actually
        reducing ulevel below 1, but include this for bulletproofing */
     if (u.ulevel < 1) {