1.3.x if-none-match only works if las-modified set

[Brian Akins]

in ngx_http_not_modified_header_filter

if (r->headers_out.status != NGX_HTTP_OK
	|| r != r->main
	|| r->headers_out.last_modified_time == -1)
    {

So, it only checks if-match or if-none-match if last-modified is set.
Is this on purpose?  I'm just wondering if we want to be able to check
etime without checking last-modified.