Fix: prevent boomerang going out of map.

From NetHack 3.7 commit 575d8c0 - caught this one while fuzzing.

Author: k21971

doc/evilhack-changelog.md

@@ -4362,4 +4362,5 @@ The following changes to date are:
 - Fix: grammar feedback when spells like barkskin or stoneskin wear off
 - Fix: portal to quest would sometimes not spawn if entry portal spawned
   on Aphrodite's Garden or the Desolate Forest levels
+- Fix: prevent boomerang going out of map
 

src/zap.c

@@ -4536,6 +4536,11 @@ int dx, dy;
         dy = ydir[i];
         bhitpos.x += dx;
         bhitpos.y += dy;
+        if (!isok(bhitpos.x, bhitpos.y)) {
+            bhitpos.x -= dx;
+            bhitpos.y -= dy;
+            break;
+        }
         if ((mtmp = m_at(bhitpos.x, bhitpos.y)) != 0) {
             m_respond(mtmp);
             tmp_at(DISP_END, 0);