fix compilation of padding_pad

... in cases where rng_get_bytes() isn't available

src/misc/padding/padding_pad.c

@@ -99,11 +99,15 @@ int padding_pad(unsigned char *data, unsigned long length, unsigned long* padded
    type = mode & LTC_PAD_MASK;
 
    if (*padded_length < l) {
+#ifdef LTC_RNG_GET_BYTES
       if (type != LTC_PAD_ISO_10126) {
          *padded_length = l;
       } else {
          *padded_length = length + 256;
       }
+#else
+      *padded_length = l;
+#endif
       return CRYPT_BUFFER_OVERFLOW;
    }