R926 - polymorphed player does not explode at thin air

Reported that player polymorphed into an exploding monster does not explode
when attacking thin air.  Also noticed that if player is Unchanging, they
wouldn't die after exploding in the existing code.  Set u.mh = -1 to ensure
they won't still be around after exploding.

doc/fixes34.1

@@ -137,6 +137,8 @@ grammar of blessed-detection eating warning messages when eating 1 of N objects
 message for charging for items lost in a cursed magic bag wasn't always shown
 dropping gold on an altar printed no message and didn't change gnostic conduct
 don't allow cursed daggers thrown by monsters to go thru closed doors
+hero polymorphed into an exploding monster should explode when attacking
+	thin air, just like the monster itself
 
 
 Platform- and/or Interface-Specific Fixes

src/hack.c

@@ -1041,13 +1041,20 @@ domove()
 	if (flags.forcefight ||
 	    /* remembered an 'I' && didn't use a move command */
 	    (glyph_is_invisible(levl[x][y].glyph) && !flags.nopick)) {
+		boolean expl = (Upolyd && attacktype(youmonst.data, AT_EXPL));
 	    	char buf[BUFSZ];
 		Sprintf(buf,"a vacant spot on the %s", surface(x,y));
-		You("attack %s.",
+		You("%s %s.",
-		    !Underwater ? "thin air" : is_pool(x,y) ? "empty water" : buf);
+		    expl ? "explode at" : "attack",
+		    !Underwater ? "thin air" :
+		    is_pool(x,y) ? "empty water" : buf);
 		unmap_object(x, y); /* known empty -- remove 'I' if present */
 		newsym(x, y);
 		nomul(0);
+		if (expl) {
+		    u.mh = -1;		/* dead in the current form */
+		    rehumanize();
+		}
 		return;
 	}
 	if (glyph_is_invisible(levl[x][y].glyph)) {

src/uhitm.c

@@ -1920,8 +1920,10 @@ use_weapon:
 			impossible("strange attack of yours (%d)",
 				 mattk->aatyp);
 	    }
-	    if (dhit == -1)
+	    if (dhit == -1) {
+		u.mh = -1;	/* dead in the current form */
 		rehumanize();
+	    }
 	    if (sum[i] == 2)
 		return((boolean)passive(mon, 1, 0, mattk->aatyp));
 							/* defender dead */