Removed double records_in_range calls from multi_range_read_info_const

This was to remove a performance regression between 10.3 and 10.4
In 10.5 we will have a better implementation of records_in_range
that will enable us to get more statistics.
This change was not done in 10.4 because the 10.5 will be part of
a larger change that is not suitable for the GA 10.4 version

Other things:
- Changed default handler block_size to 8192 to fix things statistics
  for engines that doesn't set the block size.
- Fixed a bug in spider when using multiple part const ranges
  (Patch from Kentoku)

mysql-test/main/myisam_explain_non_select_all.result

@@ -752,12 +752,12 @@ Warnings:
 Warning	1287	'<select expression> INTO <destination>;' is deprecated and will be removed in a future release. Please use 'SELECT <select list> INTO <destination> FROM...' instead
 EXPLAIN DELETE   FROM t1 WHERE t1.a > 0 ORDER BY t1.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	PRIMARY	NULL	NULL	NULL	1	Using where; Using filesort
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 FLUSH STATUS;
 FLUSH TABLES;
 EXPLAIN EXTENDED DELETE   FROM t1 WHERE t1.a > 0 ORDER BY t1.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	ALL	PRIMARY	NULL	NULL	NULL	1	100.00	Using where; Using filesort
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 # Status of EXPLAIN EXTENDED query
 Variable_name	Value
 Handler_read_key	3
@@ -781,8 +781,6 @@ Handler_read_rnd_next	1
 # Status of testing query execution:
 Variable_name	Value
 Handler_read_key	3
-Handler_read_rnd_next	1
-Sort_scan	1
 
 INSERT INTO t1 VALUES (1), (2), (3), (-1), (-2), (-3);
 #