[branch: latest develop from today] arch: Windows Issue: Cairo widgets going black

[brummer10]

I noticed a issue with cairo based plugs [vst2/3] under windows. They goes black after a short while, how fast, depend on how often they get redrawn, it seems . To get them then repaint again the host [fruity loops] needs to be restarted. This could happen to single SubWidgets as well as to the complete UI. This issue didn't happen when run under linux.