fix: fetchHostDescription don't work with Nuke

kOfxImageEffectPropOpenGLRenderSupported can be unknown to host if host doesn't support gOpenGLRenderSuite (Nuke for example)
then we can get an exception here and plugin construction will fail
so gOpenGLRenderSuite check must be done first and/or hostProps.propGetString(kOfxImageEffectPropOpenGLRenderSupported) must not raise exception