Bugfix: set errno to zero in stdio_unget_byte.

* stream.c (stdio_unget_byte): Set errno to zero before
ungetc, because ungetc probably almost certainly
doesn't set errno when it fails.

1 files changed, 1 insertions, 0 deletions

diff --git a/stream.c b/stream.c
index 60247af7..e9ba359b 100644
--- a/stream.c
+++ b/stream.c
@@ -719,6 +719,7 @@ static val stdio_unget_byte(val stream, int byte)
 {
   struct stdio_handle *h = coerce(struct stdio_handle *, stream->co.handle);
 
+  errno = 0;
   return h->f != 0 && ungetc(byte, coerce(FILE *, h->f)) != EOF
          ? num_fast(byte)
          : stdio_maybe_error(stream, lit("pushing back byte into"));