ITS#7589 another mdb_page_split fix

Tweak split_indx check, go one slot further.

libraries/liblmdb/mdb.c

@@ -7542,7 +7542,7 @@ mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno
 				psize = 0;
 				if (newindx <= split_indx || newindx >= nkeys) {
 					i = 0; j = 1;
-					k = newindx >= nkeys ? nkeys : split_indx+1;
+					k = newindx >= nkeys ? nkeys : split_indx+2;
 				} else {
 					i = nkeys; j = -1;
 					k = split_indx-1;