Details
Description
Sometimes mongoc_read_concern_destroy() triggers a segmentation fault:
mongoc_cursor_t *cursor = mongoc_collection_find(...);
// then call mongoc_cursor_more() and mongoc_cursor_next()
mongoc_cursor_destroy(cursor);
mongoc_cursor_destroy() calls mongoc_read_concern_destroy(), and the later crashes at bson_free (read_concern->level)