AppSettings: Only return true for IsD3DFullscreen() if it is actually supported.
MainFrm: Remove renderer check which is now always redundant.
MainFrm: Fix starting in fullscreen when D3DFullscreen is enabled.
MainFrm: Hide the cursor when starting in remembered fullscreen for consistency.
MainFrm: Remember last fullscreen state when using D3DFullscreen.
CVMROSD: Fix OSD message not being removed after switching the video window.
CVMROSD: Get the lock before changing the video window.