libdrgn: dwarf_index: free pending DIEs after indexing namespace

Once we've cleared the pending DIEs vector, we won't use the vector
again (unless we load more debugging information), so we can free it.

Signed-off-by: Omar Sandoval <osandov@osandov.com>

libdrgn/dwarf_index.c

@@ -2668,6 +2668,7 @@ static struct drgn_error *index_namespace(struct drgn_dwarf_index_namespace *ns)
 		return drgn_error_copy(ns->saved_err);
 	}
 	ns->pending_dies.size = 0;
+	drgn_dwarf_index_pending_die_vector_shrink_to_fit(&ns->pending_dies);
 	return err;
 }