dialog: Fix invisible dialogs when shaders aren't available
dialog: Fix invisible dialogs when shaders aren't available

If shaders/fbos aren't available, or the shader fails to compile, the
dialog wouldn't update correctly and would end up just blocking input.

pwithnall/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx