green dragon/iron golem breath

A poison gas breath attack that hits a wall would leave a 1x1 gas
cloud region at that wall spot.

Not always noticeable due to other spots along the zap path leaving
regions that blocked vision.

doc/fixes3-7-0.txt

@@ -2041,6 +2041,8 @@ priestname() didn't handle "a" vs" "an" prefix correctly; normally priests are
 	incant <scroll>."
 non-fireproof water walking boots wouldn't be burnt up if fire resistant hero
 	walked on molten lava
+1x1 poison gas clouds for green dragon and iron golem breath could be placed
+	at wall locations
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository

src/zap.c

@@ -5233,8 +5233,10 @@ zap_over_floor(
 
     case ZT_POISON_GAS:
         /* poison gas with range 1: green dragon/iron golem breath (AD_DRST);
-           caller is placing a series of 1x1 clouds along the zap's path */
+           caller is placing a series of 1x1 clouds along the zap's path;
-        (void) create_gas_cloud(x, y, 1, 8);
+           <x,y> for wall locations might be included--reject those */
+        if (ZAP_POS(lev->typ))
+            (void) create_gas_cloud(x, y, 1, 8);
         break;
 
     case ZT_LIGHTNING: