Fix ..-collapsing bug in relative URL parser

c++/src/kj/compat/url-test.c++

@@ -369,6 +369,9 @@ KJ_TEST("parse relative URL") {
   parseAndCheckRelative("https://capnproto.org/foo/bar?baz=qux#corge",
                         "/http:/grault",
                         "https://capnproto.org/http%3A/grault");
+  parseAndCheckRelative("https://capnproto.org/",
+                        "/foo/../bar",
+                        "https://capnproto.org/bar");
 }
 
 KJ_TEST("parse relative URL failure") {

c++/src/kj/compat/url.c++

@@ -312,7 +312,7 @@ Maybe<Url> Url::tryParseRelative(StringPtr text) const {
     for (;;) {
       auto part = split(text, END_PATH_PART);
       if (part.size() == 2 && part[0] == '.' && part[1] == '.') {
-        if (path.size() != 0) {
+        if (result.path.size() != 0) {
           result.path.removeLast();
         }
         result.hasTrailingSlash = true;