fix rare crash when loading a workspace
fix rare crash when loading a workspace

The crash occurs when the universes are deleted while
one is sending its dmx values.

mcallegari/qlcplus,sbenejam/qlcplus,kripton/qlcplus,mcallegari/qlcplus,plugz/qlcplus,mcallegari/qlcplus,kripton/qlcplus,mcallegari/qlcplus,sbenejam/qlcplus,sbenejam/qlcplus,sbenejam/qlcplus,plugz/qlcplus,kripton/qlcplus,nedmech/qlcplus,mcallegari/qlcplus,nedmech/qlcplus,mcallegari/qlcplus,kripton/qlcplus,plugz/qlcplus,nedmech/qlcplus,sbenejam/qlcplus,plugz/qlcplus,kripton/qlcplus,sbenejam/qlcplus,plugz/qlcplus,nedmech/qlcplus,sbenejam/qlcplus,mcallegari/qlcplus,plugz/qlcplus,kripton/qlcplus,nedmech/qlcplus,nedmech/qlcplus,kripton/qlcplus,plugz/qlcplus