tfw_http_search_cookie() may pass chunk == end, which is past the last

chunk, to tfw_str_collect_cmp(). Firstly check chunk == end in
tfw_str_collect_cmp() and only after than make an assertion that chunk
is a plain string.

fw/http_match.c

@@ -906,6 +906,7 @@ tfw_http_search_cookie(const char *cstr, unsigned long clen,
 	TfwStr *chunk, *end;
 	TfwStr tmp = { 0 };
 	unsigned int n = cookie->nchunks;
+
 	/* Search cookie name. */
 	end = cookie->chunks + cookie->nchunks;
 	for (chunk = cookie->chunks; chunk != end; ++chunk, --n) {
@@ -951,6 +952,7 @@ tfw_http_search_cookie(const char *cstr, unsigned long clen,
 			}
 
 		} else {
+			WARN_ON_ONCE(1);
 			continue;
 		}
 		/*

fw/str.c

@@ -561,12 +561,11 @@ void tfw_str_collect_cmp(TfwStr *chunk, TfwStr *end, TfwStr *out,
 {
 	TfwStr *next;
 
-	BUG_ON(!TFW_STR_PLAIN(chunk));
-
 	if (unlikely(chunk == end)) {
 		bzero_fast(out, sizeof(*out));
 		return;
 	}
+	BUG_ON(!TFW_STR_PLAIN(chunk));
 
 	/* If this is last chunk, just return it in this case. */
 	next = chunk + 1;