ITS#8857 document mdb_cursor_del does not invalidate the cursor

libraries/liblmdb/lmdb.h

@@ -1510,6 +1510,10 @@ int  mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 	/** @brief Delete current key/data pair
 	 *
 	 * This function deletes the key/data pair to which the cursor refers.
+	 * This does not invalidate the cursor, so operations such as MDB_NEXT
+	 * can still be used on it.
+	 * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after
+	 * this operation.
 	 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
 	 * @param[in] flags Options for this operation. This parameter
 	 * must be set to 0 or one of the values described here.