ITS#7598 mdb_dbi_open(named DB): Check mainDB flags.

Reject attempts to open named databases if the main
database has flag MDB_DUPSORT or MDB_INTEGERKEY.

DUPSORT would require an xcursor for the DB, INTEGERKEY
would expect the DB name to be a binary integer.

libraries/liblmdb/mdb.c

@@ -7226,6 +7226,10 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 	if (!unused && txn->mt_numdbs >= txn->mt_env->me_maxdbs)
 		return MDB_DBS_FULL;
 
+	/* Cannot mix named databases with some mainDB flags */
+	if (txn->mt_dbs[MAIN_DBI].md_flags & (MDB_DUPSORT|MDB_INTEGERKEY))
+		return (flags & MDB_CREATE) ? MDB_INCOMPATIBLE : MDB_NOTFOUND;
+
 	/* Find the DB info */
 	dbflag = DB_NEW|DB_VALID;
 	exact = 0;