fread does not return negative on error

size_t res cannot be less than 0. fread returns 0 on error.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/strbuf.c b/strbuf.c
index a884960..f03d117 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -260,7 +260,7 @@
 	res = fread(sb->buf + sb->len, 1, size, f);
 	if (res > 0)
 		strbuf_setlen(sb, sb->len + res);
-	else if (res < 0 && oldalloc == 0)
+	else if (oldalloc == 0)
 		strbuf_release(sb);
 	return res;
 }