http-fetch: Tidy control flow in process_alternate_response

It's a bit convoluted.  Tidy it up.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

http-fetch.c

@@ -468,13 +468,11 @@ static void process_alternates_response(void *callback_data)
 					 alt_req->url);
 			active_requests++;
 			slot->in_use = 1;
-			if (start_active_slot(slot)) {
+			if (!start_active_slot(slot)) {
-				return;
-			} else {
 				got_alternates = -1;
 				slot->in_use = 0;
-				return;
 			}
+			return;
 		}
 	} else if (slot->curl_result != CURLE_OK) {
 		if (slot->http_code != 404 &&