strbuf: avoid redundant reset in strbuf_getwholeline()

The HAVE_GETDELIM variant of strbuf_getwholeline() calls strbuf_reset()
on the strbuf before handing it over to getdelim(3).  This is
unnecessary:

  - getdelim(3) doesn't care whether the old buffer contents is
    NUL-terminated and has no access to ->len,
  - on success getdelim(3) NUL-terminates the buffer and we set ->len,
  - on error we either call strbuf_init() or strbuf_reset().

Remove the superfluous preparatory call.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -646,8 +646,6 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
 	if (feof(fp))
 		return EOF;
 
-	strbuf_reset(sb);
-
 	/* Translate slopbuf to NULL, as we cannot call realloc on it */
 	if (!sb->alloc)
 		sb->buf = NULL;