Bug#40954: Crash in MyISAM index code with concurrency test using partitioned tables

Problem was usage of read_range_first with an empty key.

Solution was to not to give a key if it was empty.

mysql-test/r/partition.result:
  Bug#40954: Crash in MyISAM index code with concurrency test using partitioned tables
  
  Updated test result.
mysql-test/t/partition.test:
  Bug#40954: Crash in MyISAM index code with concurrency test using partitioned tables
  
  Added test case

mysql-test/r/partition.result

 drop table if exists t1, t2;
+CREATE TABLE t1 (
+pk INT NOT NULL AUTO_INCREMENT,
+PRIMARY KEY (pk)
+)
+/*!50100 PARTITION BY HASH (pk)
+PARTITIONS 2 */;
+INSERT INTO t1 VALUES (NULL);
+INSERT INTO t1 VALUES (NULL);
+INSERT INTO t1 VALUES (NULL);
+SELECT * FROM t1 WHERE pk < 0 ORDER BY pk;
+pk
+DROP TABLE t1;
 CREATE TABLE t1 (a INT NOT NULL, KEY(a))
 PARTITION BY RANGE(a)
 (PARTITION p1 VALUES LESS THAN (200), PARTITION pmax VALUES LESS THAN MAXVALUE);

mysql-test/t/partition.test

@@ -14,6 +14,21 @@
 drop table if exists t1, t2;
 --enable_warnings
 
+#
+# Bug#40954: Crash if range search and order by.
+#
+CREATE TABLE t1 (
+  pk INT NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY (pk)
+)
+/*!50100 PARTITION BY HASH (pk)
+PARTITIONS 2 */;
+INSERT INTO t1 VALUES (NULL);
+INSERT INTO t1 VALUES (NULL);
+INSERT INTO t1 VALUES (NULL);
+SELECT * FROM t1 WHERE pk < 0 ORDER BY pk;
+DROP TABLE t1;
+
 #
 # Bug#40494: Crash MYSQL server crashes on range access with partitioning
 #            and order by

sql/ha_partition.cc

@@ -4490,7 +4490,8 @@ int ha_partition::handle_ordered_index_scan(uchar *buf, bool reverse_order)
         This can only read record to table->record[0], as it was set when
         the table was being opened. We have to memcpy data ourselves.
       */
-      error= file->read_range_first(&m_start_key, end_range, eq_range, TRUE);
+      error= file->read_range_first(m_start_key.key? &m_start_key: NULL,
+                                    end_range, eq_range, TRUE);
       memcpy(rec_buf_ptr, table->record[0], m_rec_length);
       reverse_order= FALSE;
       break;