[vte] build: Fix vteconv warning

[Egmont Koblinger <egmontkob src gnome org>]

commit 3fe609d9592b69854796cdc1011d0112bc7506af
Author: Egmont Koblinger <egmont gmail com>
Date:   Fri May 16 13:57:01 2014 +0200

    build: Fix vteconv warning

 src/vteconv.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/vteconv.c b/src/vteconv.c
index 2709793..dcf4fd7 100644
--- a/src/vteconv.c
+++ b/src/vteconv.c
@@ -389,7 +389,8 @@ main(int argc, char **argv)
        gunichar wide_test[5];
        gchar narrow_test[5], buf[10];
        VteConv conv;
-       gchar *inbuf, *outbuf;
+       const guchar *inbuf;
+       guchar *outbuf;
        gsize inbytes, outbytes;
        char mbyte_test[] = {0xe2, 0x94, 0x80};
        char mbyte_test_break[] = {0xe2, 0xe2, 0xe2};