Fix buffer over-read in percent_decode().

When decoding a trigram, percent_decode() would correctly increment the input pointer by an extra two characters (three total) but would not decrement the input length by the same amount.  This would result in a buffer over-read when decoding unterminated strings.

lib/enc/cryb_percent.c

@@ -92,6 +92,7 @@ percent_decode(const char *in, size_t ilen, char *out, size_t *olen)
 			if (++len < *olen && out != NULL)
 				*out++ = unhex(in[1]) << 4 | unhex(in[2]);
 			in += 2;
+			ilen -= 2;
 		} else {
 			if (*olen > 0 && out != NULL)
 				*out = '\0';