MDEV-13748 Assertion `status_var.local_memory_used == 0 ||...

MDEV-13748 Assertion `status_var.local_memory_used == 0 || !debug_assert_on_not_freed_memory' failed in virtual THD::~THD after query with INTERSECT

my_safe_alloca()/my_safe_afree() work as alloca() or malloc()/free()
depending on the memory size to allocate, that is, depending on
reclength here. They only work correctly if reclength doesn't
change in the middle.

mysql-test/suite/maria/dynamic.result

+create table t1 (a blob, b varchar(20000)) engine=aria row_format=dynamic;
+insert t1 (b) values (repeat('a', 20000));
+update t1 set b='b';
+drop table t1;

mysql-test/suite/maria/dynamic.test

+#
+# MDEV-13748 Assertion `status_var.local_memory_used == 0 || !debug_assert_on_not_freed_memory' failed in virtual THD::~THD after query with INTERSECT
+#
+create table t1 (a blob, b varchar(20000)) engine=aria row_format=dynamic;
+insert t1 (b) values (repeat('a', 20000));
+update t1 set b='b';
+drop table t1;

storage/maria/ma_dynrec.c

@@ -276,7 +276,7 @@ my_bool _ma_update_blob_record(MARIA_HA *info, MARIA_RECORD_POS pos,
 {
   uchar *rec_buff;
   int error;
-  ulong reclength,extra;
+  ulong reclength,reclength2,extra;
 
   extra= (ALIGN_SIZE(MARIA_MAX_DYN_BLOCK_HEADER)+MARIA_SPLIT_LENGTH+
 	  MARIA_DYN_DELETE_BLOCK_HEADER);
@@ -289,17 +289,17 @@ my_bool _ma_update_blob_record(MARIA_HA *info, MARIA_RECORD_POS pos,
     return 1;
   }
 #endif
-  if (!(rec_buff=(uchar*) my_safe_alloca(reclength,
-                                         MARIA_MAX_RECORD_ON_STACK)))
+  if (!(rec_buff=(uchar*) my_safe_alloca(reclength, MARIA_MAX_RECORD_ON_STACK)))
   {
     my_errno= HA_ERR_OUT_OF_MEM; /* purecov: inspected */
     return(1);
   }
-  reclength= _ma_rec_pack(info,rec_buff+ALIGN_SIZE(MARIA_MAX_DYN_BLOCK_HEADER),
+  reclength2= _ma_rec_pack(info,rec_buff+ALIGN_SIZE(MARIA_MAX_DYN_BLOCK_HEADER),
 			 record);
+  DBUG_ASSERT(reclength2 <= reclength);
   error=update_dynamic_record(info,pos,
 			      rec_buff+ALIGN_SIZE(MARIA_MAX_DYN_BLOCK_HEADER),
-			      reclength);
+			      reclength2);
   my_safe_afree(rec_buff, reclength, MARIA_MAX_RECORD_ON_STACK);
   return(error != 0);
 }