qml value provider not cleaned up in statically linked Qt

QQuick_initializeProviders installs a ValueTypeProvider, however QQuick_deinitializeProviders is never called. following calls to QQuick_initializeProviders will therefore install the same instance in QQml_addValueTypeProvider, causing a cyclic list. This causes a live-lock in all QQmlValueTypeProvider API functions, which try to iterate through the cyclic list.

This typically occurs when using qml inside a plugin: it live-locks after the plugin is initialised the second time after not completely being unloaded (which under osx is quite common).

QTBUG-43004 is about the same issue with dynamically loaded plugins. its fix does not apply for static plugins, though.