Fix htable cleanup (JuliaLang#44446)

This htable was allocated conditionally, so the cleanup must be too.

Co-authored by: Jameson Nash <[email protected]>

src/dump.c

@@ -312,8 +312,8 @@ static size_t queue_external_mis(jl_array_t *list)
  }
  }
  }
+ htable_free(&visited);
  }
- htable_free(&visited);
  return n;
 }