Resolve "fix ogre application crash on macos"

What does this MR do?

Fix various crash as reported by https://gitlab.lan.local/Sight/sight/issues/129:

• Correct shader compilation errors.
• Fix opengl context corruption

How to test it?

Launch OgreViewer, play a bit with it, especially with the "CompositorSelector".

Additional tests to run

• Windows
• Macos
• Linux