Replace awful "You feel cold" message for freezing a door you can't see

That message implied something to do with an effect happening to the
hero that causes them to feel cold, such as taking cold damage.
Change it to "You hear a deep cracking sound" instead.

src/zap.c

@@ -4626,7 +4626,7 @@ short exploding_wand_typ;
         case ZT_COLD:
             new_doormask = D_NODOOR;
             see_txt = "The door freezes and shatters!";
-            sense_txt = "feel cold.";
+            hear_txt = "a deep cracking sound.";
             break;
         case ZT_DEATH:
             /* death spells/wands don't disintegrate */