Prevent blinding ray at yourself

The code doesn't handle zapping blinding ray at yourself;
maybe it should be changed to handle it, but for now just
prevent Sunsword blinding the hero.

src/artifact.c

@@ -1917,7 +1917,7 @@ arti_invoke(struct obj *obj)
             break;
         }
         case BLINDING_RAY:
-            if (getdir((char *) 0))
+            if (getdir((char *) 0) && (u.dx || u.dy))
                 do_blinding_ray(obj);
             break;
         }