Fix htable cleanup (#44446)

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

Co-authored by: Jameson Nash <jameson@juliacomputing.com>

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;
 }