CookieJar: Clear filter function in destructor

Fixes possible crash when cookieFilter is called after CookieJar
was destroyed.

src/lib/cookies/cookiejar.cpp

@@ -44,6 +44,13 @@ CookieJar::CookieJar(QObject* parent)
     connect(m_client, &QWebEngineCookieStore::cookieRemoved, this, &CookieJar::slotCookieRemoved);
 }
 
+CookieJar::~CookieJar()
+{
+#if QT_VERSION >= QT_VERSION_CHECK(5, 11, 0)
+    m_client->setCookieFilter(nullptr);
+#endif
+}
+
 void CookieJar::loadSettings()
 {
     Settings settings;

src/lib/cookies/cookiejar.h

@@ -32,6 +32,7 @@ class FALKON_EXPORT CookieJar : public QObject
 
 public:
     explicit CookieJar(QObject* parent = 0);
+    ~CookieJar();
 
     void loadSettings();