compositor: add safety check when EGL fails to initialize

offending message:

    Program received signal SIGSEGV, Segmentation fault.
    create_pointer_images (ec=0x619f10) at compositor.c:240
    240         glEGLImageTargetTexture2DOES(GL_TEXTURE_2D,

Signed-off-by: Tiago Vignatti <tiago.vignatti@nokia.com>