[libxml2] Fix unused parameter warning without ICU

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 772c06487b45d347d8c1387a217d930f6ab485d0
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Thu Nov 9 17:56:31 2017 +0100

    Fix unused parameter warning without ICU

 encoding.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/encoding.c b/encoding.c
index 5dac8a1..de7b511 100644
--- a/encoding.c
+++ b/encoding.c
@@ -1916,6 +1916,7 @@ static int
 xmlEncInputChunk(xmlCharEncodingHandler *handler, unsigned char *out,
                  int *outlen, const unsigned char *in, int *inlen, int flush) {
     int ret;
+    (void)flush;
 
     if (handler->input != NULL) {
         ret = handler->input(out, outlen, in, inlen);