ITS#7943 reinit txn flags

When reusing the main write txn

libraries/liblmdb/mdb.c

@@ -2626,6 +2626,7 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 	if (!(flags & MDB_RDONLY)) {
 		if (!parent) {
 			txn = env->me_txn0;
+			txn->mt_flags = 0;
 			goto ok;
 		}
 		size += env->me_maxdbs * sizeof(MDB_cursor *);