Patching libgltf: shader character buffers are used as c strings

Change-Id: Ic0c2bd47ffd5bf2d12e2201063ca688712a5f9b3
Make OGLFrameGrabber work

Steps of grabFrame
- Init opengl context
- Call libgltf to render
- Get a RGB buffer from libgltf
- Create a Bitmap from this RGB buffer

Additionally:
- Using mimetype is neccessary to decide which player to create.
- bAllowToCreateReplacementGraphic is unneeded.

Change-Id: I7fef043a3341771389144a4f4cac71b0862ef8a7