AutoTest: Fix persisting of check states

Persistent settings cannot handle QVariantHash and when
reading the check state the meta type system seems to have
the need to have used the check state already before,
otherwise it will fail to convert until it uses it.
This happened e.g. when re-opening a project that had
former check states stored inside the project settings
directly from the Welcome page after starting QC.
Amends df49d6e40d.

Change-Id: Id2b85373c151efb5890fe5fb7392bdbc11adda50
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/autotest/autotestplugin.cpp

@@ -118,6 +118,8 @@ AutotestPlugin::AutotestPlugin()
     qRegisterMetaType<TestResult>();
     qRegisterMetaType<TestTreeItem *>();
     qRegisterMetaType<TestCodeLocationAndType>();
+    // warm up meta type system to be able to read Qt::CheckState with persistent settings
+    qRegisterMetaType<Qt::CheckState>();
 }
 
 AutotestPlugin::~AutotestPlugin()