Fix crash in _IO_wfile_sync (bug 20568)

When computing the length of the converted part of the stdio buffer, use
the number of consumed wide characters, not the (negative) distance to the
end of the wide buffer.

1 files changed, 1 insertions, 0 deletions

diff --git a/libio/tst-wfile-sync.input b/libio/tst-wfile-sync.input
new file mode 100644
index 0000000..12d0958
--- /dev/null
+++ b/libio/tst-wfile-sync.input
@@ -0,0 +1 @@
+This is a test of _IO_wfile_sync.