MSVS2013 was warning about implicit conversion from EGLint to bool.
Fix this by making the conversion explicit like another similar
conversions.

The issue got introduced by the recent patch "Implement
EGL_ANGLE_direct_composition extension". Since the issue only affects
some particular build varieties, it's simpler to fix it rather than
revert the patch.

Change-Id: I120d34fddb48278856cbb0339ce25c49e57eb781
Reviewed-on: https://chromium-review.googlesource.com/320530Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>