loader.c: Use our ishex() instead of strspn(3) in PWDUMP detection

This is to have predictably low performance impact of these checks,
regardless of what case libc's strspn() is optimized for.

See openwall#5328, amends f3a01f5

Author: solardiz

src/loader.c

@@ -37,6 +37,7 @@
 #include "dyna_salt.h"
 #include "loader.h"
 #include "options.h"
+#include "common.h"
 #include "config.h"
 #include "unicode.h"
 #include "dynamic.h"
@@ -603,8 +604,8 @@ static int ldr_split_line(char **login, char **ciphertext,
 	if (SPLFLEN(1) > MAX_CIPHERTEXT_SIZE) {
 		huge_line = 1;
 	}
-	else if ((SPLFLEN(3) == 32 && strspn(fields[3], HEXCHARS_all) == 32) ||
-	         (SPLFLEN(2) == 32 && strspn(fields[2], HEXCHARS_all) == 32)) {
+	else if ((SPLFLEN(3) == 32 && ishex(fields[3])) ||
+	         (SPLFLEN(2) == 32 && ishex(fields[2]))) {
 		/* PWDUMP */
 		/* user:uid:LMhash:NThash:comment:homedir: */
 		*uid = fields[1];