ITS#7377 Catch MDB failure updating root pointers.

"cannot fail" was wrong, it fails at least when exceeding mapsize.

libraries/liblmdb/mdb.c

@@ -2124,9 +2124,7 @@ mdb_txn_commit(MDB_txn *txn)
 	DPRINTF("committing txn %zu %p on mdbenv %p, root page %zu",
 	    txn->mt_txnid, (void *)txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root);
 
-	/* Update DB root pointers. Their pages have already been
+	/* Update DB root pointers */
-	 * touched so this is all in-place and cannot fail.
-	 */
 	if (txn->mt_numdbs > 2) {
 		MDB_dbi i;
 		MDB_val data;
@@ -2136,7 +2134,9 @@ mdb_txn_commit(MDB_txn *txn)
 		for (i = 2; i < txn->mt_numdbs; i++) {
 			if (txn->mt_dbflags[i] & DB_DIRTY) {
 				data.mv_data = &txn->mt_dbs[i];
-				mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
+				rc = mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
+				if (rc)
+					goto fail;
 			}
 		}
 	}