fix crash in handle_wants_lookat/trans.up() when trans.translation is 0

src/actor.rs

@@ -624,7 +624,12 @@ fn handle_wants_lookat(
         } else {
             continue;
         };
-        rot.0 = look_at_quat(**pos, target_pos, trans.up().as_dvec3());
+        let up = if trans.translation.length_squared() > 1e-6 {
+            trans.up()
+        } else {
+            Dir3::Y
+        };
+        rot.0 = look_at_quat(**pos, target_pos, up.as_dvec3());
     }
 }