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>
diff --git a/cgit.c b/cgit.c
index 29e075d..04682be 100644
--- a/cgit.c
+++ b/cgit.c
@@ -37,10 +37,10 @@
 
 	switch (filtertype) {
 		case SOURCE:
+		case ABOUT:
 			extra_args = 1;
 			break;
 
-		case ABOUT:
 		case COMMIT:
 		default:
 			extra_args = 0;