Bug#8840 Empty string comparison and character set 'cp1250'

Secondary weight out of bounds was picked up in mistake when
the string is empty, instead of returning 0.

mysql-test/include/have_cp1250_ch.inc

+-- require r/have_cp1250_ch.require
+disable_query_log;
+show collation like "cp1250_czech_cs";
+enable_query_log;

mysql-test/r/ctype_cp1250_ch.result

+SHOW COLLATION LIKE 'cp1250_czech_cs';
+Collation	Charset	Id	Default	Compiled	Sortlen
+cp1250_czech_cs	cp1250	34		Yes	2
+CREATE TABLE t1 (a char(16)) character set cp1250 collate cp1250_czech_cs;
+INSERT INTO t1 VALUES ('');
+SELECT a, length(a), a='', a=' ', a='  ' FROM t1;
+a	length(a)	a=''	a=' '	a='  '
+	0	1	1	1
+DROP TABLE t1;

mysql-test/r/have_cp1250_ch.require

+Collation	Charset	Id	Default	Compiled	Sortlen
+cp1250_czech_cs	cp1250	34		Yes	2

mysql-test/t/ctype_cp1250_ch.test

+-- source include/have_cp1250_ch.inc
+
+SHOW COLLATION LIKE 'cp1250_czech_cs';
+
+#
+# Bugs: #8840: Empty string comparison and character set 'cp1250'
+#
+
+CREATE TABLE t1 (a char(16)) character set cp1250 collate cp1250_czech_cs;
+INSERT INTO t1 VALUES ('');
+SELECT a, length(a), a='', a=' ', a='  ' FROM t1;
+DROP TABLE t1;

strings/ctype-win1250ch.c

@@ -416,7 +416,7 @@ static struct wordvalue doubles[] = {
 #define NEXT_CMP_VALUE(src, p, pass, value, len)			\
 	while (1) {							\
 		if (IS_END(p, src, len)) {				\
-			if (pass == 0) { p = src; pass++; }		\
+			if (pass == 0 && len > 0) { p= src; pass++; }	\
 			else { value = 0; break; }			\
 		}							\
 		value = ((pass == 0) ? _sort_order_win1250ch1[*p]	\