set errno in null cases, just in case.

src/lib/libc/crypt/crypt.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: crypt.c,v 1.28 2015/05/13 21:01:54 bluhm Exp $	*/
+/*	$OpenBSD: crypt.c,v 1.29 2015/07/18 00:58:19 tedu Exp $	*/
 
 #include <pwd.h>
 
@@ -10,9 +10,10 @@ crypt(const char *key, const char *setting)
 		case '2':
 			return bcrypt(key, setting);
 		default:
+			errno = EINVAL;
 			return (NULL);
 		}
 	}
-
+	errno = EINVAL;
 	return (NULL);
 }