fix issue #1453 - throwing crackable object upward

Issue reported by NullCGT:  throwing a crackable item against the
ceiling would cause it to vanish if it became [more] cracked but not
yet fully shattered.

Fixes #1453

doc/fixes3-7-0.txt

@@ -2133,6 +2133,8 @@ mounted hero was able to deliver joust hits when trapped
 timer sanity check for melting ice gave false complaint about non-ice for
 	frozen moat under open drawbridge
 mhitm_ad_phys() was not applying Half_physical_damage when hero was target
+throwing crystal plate mail or helm of brilliance up against the ceiling could
+	result in the item being cracked and then vanishing
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository

src/dothrow.c

@@ -1268,7 +1268,14 @@ toss_up(struct obj *obj, boolean hitsroof)
         if (breaktest(obj)) {
             pline("%s hits the %s.", Doname2(obj), ceiling(u.ux, u.uy));
             breakmsg(obj, !Blind);
-            return breakobj(obj, u.ux, u.uy, TRUE, TRUE) ? FALSE : TRUE;
+            /* crackable armor will return True for breaktest() but will
+               usually return False for breakobj() */
+            if (!breakobj(obj, u.ux, u.uy, TRUE, TRUE)) {
+                hitfloor(obj, FALSE);
+                gt.thrownobj = 0;
+                return TRUE;
+            }
+            return FALSE;
         }
         action = "hits";
     } else {