ui-summary: Pass filename to about-filter

This gives the about-filter API the same semantics as source-filter,
where the filter receives the filename so it can decide what to do next
with it.

While we're at it, plug a memory leak.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui-repolist.c

@@ -332,9 +332,13 @@ void cgit_print_site_readme()
 {
 	if (!ctx.cfg.root_readme)
 		return;
-	if (ctx.cfg.about_filter)
+	if (ctx.cfg.about_filter) {
+		ctx.cfg.about_filter->argv[1] = ctx.cfg.root_readme;
 		cgit_open_filter(ctx.cfg.about_filter);
+	}
 	html_include(ctx.cfg.root_readme);
-	if (ctx.cfg.about_filter)
+	if (ctx.cfg.about_filter) {
 		cgit_close_filter(ctx.cfg.about_filter);
+		ctx.cfg.about_filter->argv[1] = NULL;
+	}
 }