Fix crashes in QQuickWebEngineSettings

Remove QQuickWebEngineSettingsPrivate object's pointer from the global
setting list before the object is destructed.

Change-Id: I1cca6bf8aa2438903692d9e2ef863c8fc543adbd
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Disable error page while testing loadFail signal of Quick API

Error page should be disabled while testing loadFail signal since
testing signals of the internal error page is not possible yet.

Change-Id: I07f0bb6378fcbf5d18634197808801c94606803c
Reviewed-by: Andras Becsi <andras.becsi@digia.com>