Fix thirdParty setting for first party request

Some first party requests has no site_for_cookies yet, and thus returns
an empty string. The logic matches that of StaticCookiePolicy.

Change-Id: I10caf978dc410639cd21fc2aa01eb2bf6dc67c1f
Fixes: QTBUG-71393
Reviewed-by: Jüri Valdmann <[email protected]>

Author: Allan Sandfeld Jensen

src/core/api/qwebenginecookiestore.cpp

@@ -196,7 +196,8 @@ bool QWebEngineCookieStorePrivate::canAccessCookies(const QUrl &firstPartyUrl, c
     if (!filterCallback)
         return true;
 
-    bool thirdParty =
+    // Empty first-party URL indicates a first-party request (see net/base/static_cookie_policy.cc)
+    bool thirdParty = !firstPartyUrl.isEmpty() &&
             !net::registry_controlled_domains::SameDomainOrHost(toGurl(url),
                                                                 toGurl(firstPartyUrl),
                                                                 net::registry_controlled_domains::INCLUDE_PRIVATE_REGISTRIES);