sha1_file: typofix

The number zero is spelled "zero", not "zer0".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -1308,7 +1308,7 @@ static void *unpack_sha1_rest(z_stream *stream, void *buffer, unsigned long size
 		/*
 		 * The above condition must be (bytes <= size), not
 		 * (bytes < size).  In other words, even though we
-		 * expect no more output and set avail_out to zer0,
+		 * expect no more output and set avail_out to zero,
 		 * the input zlib stream may have bytes that express
 		 * "this concludes the stream", and we *do* want to
 		 * eat that input.