check pw_passwd != NULL here too

Again, for systems with broken NIS implementations.

Prompted by coolbugcheckers AT gmail.com
diff --git a/auth-passwd.c b/auth-passwd.c
index 65f5251..24fcb67 100644
--- a/auth-passwd.c
+++ b/auth-passwd.c
@@ -198,6 +198,9 @@
 	/* Just use the supplied fake password if authctxt is invalid */
 	char *pw_password = authctxt->valid ? shadow_pw(pw) : pw->pw_passwd;
 
+	if (pw_password == NULL)
+		return 0;
+
 	/* Check for users with no password. */
 	if (strcmp(pw_password, "") == 0 && strcmp(password, "") == 0)
 		return (1);