When no UIThread is set, act as if xwt wasn't initialized and execute directly every queued Task.
When no UIThread is set, act as if xwt wasn't initialized and execute directly every queued Task.

This allows unit test on parts that use the scheduler to run even without a main loop available.

directhex/xwt,cra0zy/xwt,hwthomas/xwt,steffenWi/xwt,sevoku/xwt,akrisiun/xwt,mminns/xwt,antmicro/xwt,TheBrainTech/xwt,mono/xwt,hamekoz/xwt,iainx/xwt,mminns/xwt,residuum/xwt,lytico/xwt