Fix QWebEnginePage emit zero loadProgress before loadStarted

Restore expected behavior for QWebEnginePage loading progress. This was
missing after queuing progress notification signals change. Add missing
state transition to loadSignalsOrder test.

Change-Id: Id1d94f8391b83decc8057c5108d2d19c38258965
Reviewed-by: Michael Brüning <michael.bruning@qt.io>
Reviewed-by: Michal Klocek <michal.klocek@qt.io>