Fixed assert in Aria on SHOW PROCEDURE STATUS

MDEV-18457 Assertion `(bitmap->map +
           (bitmap->full_head_size/6*6)) <= full_head_end failed

The problem was that full_head_size was not calculated correctly
in the case when insert_order was inforced, which is the case
for SHOW commands.

mysql-test/r/sp2.result

+CREATE DATABASE test1;
+CREATE PROCEDURE test1.sp3() BEGIN END;
+SHOW PROCEDURE STATUS;
+Db	Name	Type	Definer	Modified	Created	Security_type	Comment	character_set_client	collation_connection	Database Collation
+mtr	add_suppression	PROCEDURE	root@localhost	#	#	DEFINER		utf8	utf8_general_ci	latin1_swedish_ci
+mtr	check_testcase	PROCEDURE	root@localhost	#	#	DEFINER		utf8	utf8_general_ci	latin1_swedish_ci
+mtr	check_warnings	PROCEDURE	root@localhost	#	#	DEFINER		utf8	utf8_general_ci	latin1_swedish_ci
+mysql	AddGeometryColumn	PROCEDURE	root@localhost	#	#	INVOKER		latin1	latin1_swedish_ci	latin1_swedish_ci
+mysql	DropGeometryColumn	PROCEDURE	root@localhost	#	#	INVOKER		latin1	latin1_swedish_ci	latin1_swedish_ci
+test	sp2	PROCEDURE	root@localhost	#	#	DEFINER		latin1	latin1_swedish_ci	latin1_swedish_ci
+test1	sp1	PROCEDURE	root@localhost	#	#	DEFINER		latin1	latin1_swedish_ci	latin1_swedish_ci
+test1	sp3	PROCEDURE	root@localhost	#	#	DEFINER		latin1	latin1_swedish_ci	latin1_swedish_ci
+DROP PROCEDURE sp2;
+DROP DATABASE test1;
+select count(*) from mysql.event;
+count(*)
+416
+flush tables;
+show events;
+truncate table mysql.event;

storage/maria/ma_bitmap.c

@@ -1288,6 +1288,7 @@ static my_bool allocate_head(MARIA_FILE_BITMAP *bitmap, uint size,
     uint byte= 6 * (last_insert_page / 16);
     first_pattern= last_insert_page % 16;
     data= bitmap->map+byte;
+    first_found= 0;                         /* Don't update full_head_size */
     DBUG_ASSERT(data <= end);
   }
   else