Add missing break

A rolling boulder hitting a wall or a tree could keep going,
possibly going out of map bounds

src/trap.c

@@ -3384,6 +3384,7 @@ launch_obj(
                 if (!Deaf)
                     pline("Thump!");
                 wake_nearto(x2, y2, 16);
+                break;
             }
         }
     } /* while dist > 0 */