MDEV-14667 Assertion `used_parts > 0' failed in ha_partition::init_record_priority_queue.

Do not fail fi all the partitions were pruned out.

mysql-test/main/partition_pruning.result

@@ -3485,6 +3485,16 @@ a	b	c	d
 1	a	b	1
 drop table t1;
 #
+# MDEV-14667 Assertion `used_parts > 0' failed in ha_partition::init_record_priority_queue.
+#
+create table t1 (a int);
+insert into t1 values (1),(2);
+create table t2 (b int, c int, key(c,b)) partition by hash(b) partitions 2;
+insert into t2 values (3,4),(5,6);
+select straight_join * from t1, t2 where b != NULL;
+a	b	c
+drop table t1, t2;
+#
 # MDEV-17493: Partition pruning doesn't work for nested outer joins
 #
 create table t0(a int);

mysql-test/main/partition_pruning.test

@@ -1536,6 +1536,19 @@ select * from t1 where (a = 1 AND b < 'd' AND (c = 'b' OR (c = 'c' AND d = 1)) O
                        (a = 1 AND b >= 'a' AND (c = 'c' OR (c = 'd' AND d = 2))));
 drop table t1;
 
+--echo #
+--echo # MDEV-14667 Assertion `used_parts > 0' failed in ha_partition::init_record_priority_queue.
+--echo #
+
+create table t1 (a int);
+insert into t1 values (1),(2);
+
+create table t2 (b int, c int, key(c,b)) partition by hash(b) partitions 2;
+insert into t2 values (3,4),(5,6);
+
+select straight_join * from t1, t2 where b != NULL;
+drop table t1, t2;
+
 --echo #
 --echo # MDEV-17493: Partition pruning doesn't work for nested outer joins
 --echo #

sql/ha_partition.cc

@@ -5265,7 +5265,10 @@ bool ha_partition::init_record_priority_queue()
   {
     size_t alloc_len;
     uint used_parts= bitmap_bits_set(&m_part_info->read_partitions);
-    DBUG_ASSERT(used_parts > 0);
+
+    if (used_parts == 0) /* Do nothing since no records expected. */
+      DBUG_RETURN(false);
+
     /* Allocate record buffer for each used partition. */
     m_priority_queue_rec_len= m_rec_length + PARTITION_BYTES_IN_POS;
     if (!m_using_extended_keys)