fix DumpHeaders duplicated cookies (#599)

Co-authored-by: llx <llx@U-Q6Q0149D-2359.local>

http/Http1Parser.h

@@ -28,6 +28,9 @@ public:
                 HttpCookie cookie;
                 if (cookie.parse(header_value)) {
                     parsed->cookies.emplace_back(cookie);
+                    header_field.clear();
+		    header_value.clear();
+	            return;
                 }
             }
             parsed->headers[header_field] = header_value;