Fixing issue #2236 in WindowsGL

	GamePlatform.cs
	Line 284: Removed IsActive = true;

	OpenTKGamePlatform.cs
	Line 145: Runloop - added IsActive = true;

Fixes issue #2236 - Game Deactivate fired during startup.
Makes IsActive only get set to true after initialization when the game actually becomes active.

Signed-off-by: Daniel Shumway <shumway.danny@gmail.com>