fix #324: HttpCookie supports saving multiple names

http/HttpMessage.cpp

@@ -72,7 +72,7 @@ bool HttpCookie::parse(const std::string& str) {
 }
 
 std::string HttpCookie::dump() const {
-    assert(!name.empty());
+    assert(!name.empty() || !kv.empty());
     std::string res;
 
     if (!name.empty()) {