* GLControl.cs: More defensive checks for null GraphicsModes.
Set flags, context version and GraphicsMode before calling
InitializeComponents(), as the latter might cause the context to be
created (and we need this information before creating the context).
Fixes ArgumentNullException on Linux.
members are accessed (issue [#1141]: "Unhandled exception in
GlControl possible bug in rev 2207"). Throw ObjectDisposedException
if public members are accessed after the GLControl has been
disposed. Force the create/recreation of the control if a public
member is called and the control handle or context does not exist.
