MDEV-15245: Assertion `false' failed in myrocks::ha_rocksdb::position

Don't call handler->position() if the last call to read a row did
not succeed.

sql/sql_select.cc

@@ -18724,7 +18724,7 @@ sub_select(JOIN *join,JOIN_TAB *join_tab,bool end_of_records)
       skip_over= FALSE;
     }
 
-    if (join_tab->keep_current_rowid)
+    if (join_tab->keep_current_rowid && !error)
       join_tab->table->file->position(join_tab->table->record[0]);
     
     rc= evaluate_join_record(join, join_tab, error);

storage/rocksdb/mysql-test/rocksdb/r/rocksdb_parts.result

@@ -135,3 +135,17 @@ SELECT 1;
 1
 1
 DROP TABLE t1;
+#
+# MDEV-15245: Assertion `false' failed in myrocks::ha_rocksdb::position
+#
+CREATE TABLE t1 (a INT) ENGINE=RocksDB;
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (b INT) ENGINE=RocksDB 
+PARTITION BY RANGE(b) 
+(PARTITION p0 VALUES LESS THAN (1), 
+PARTITION p1 VALUES LESS THAN MAXVALUE);
+INSERT INTO t2 VALUES (NULL),(0);
+CREATE ALGORITHM = MERGE VIEW v1 AS SELECT t2.* FROM t1, t2;
+UPDATE v1 SET b = 5;
+drop view v1;
+drop table t1,t2;

storage/rocksdb/mysql-test/rocksdb/t/rocksdb_parts.test

@@ -139,3 +139,22 @@ ALTER TABLE t1 ADD PARTITION PARTITIONS 2;
 SELECT 1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-15245: Assertion `false' failed in myrocks::ha_rocksdb::position
+--echo #
+CREATE TABLE t1 (a INT) ENGINE=RocksDB;
+INSERT INTO t1 VALUES (1),(2);
+# partitioning
+CREATE TABLE t2 (b INT) ENGINE=RocksDB 
+PARTITION BY RANGE(b) 
+(PARTITION p0 VALUES LESS THAN (1), 
+ PARTITION p1 VALUES LESS THAN MAXVALUE);
+
+
+INSERT INTO t2 VALUES (NULL),(0);
+CREATE ALGORITHM = MERGE VIEW v1 AS SELECT t2.* FROM t1, t2;
+UPDATE v1 SET b = 5;
+
+drop view v1;
+drop table t1,t2;
+