m.nviz.image: clean up resources

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@52304 15284696-431f-4ddb-bdfa-cd5b030d7da7

misc/m.nviz.image/main.c

@@ -233,6 +233,7 @@ int main(int argc, char *argv[])
 
     G_done_msg(_("File <%s> created."), output_name);
 
+    Nviz_destroy_data(&data);
     Nviz_destroy_render_window(offscreen);
 
     G_free((void *)output_name);