Querying the draw buffer states of the default framebuffer would lead to
crashes because it only had one state.  The spec says that all non-zero
attachments default to GL_NONE and makes no mention of special cased
errors for querying the default framebuffer.

Also fix the validation to check for extensions and ES version when
querying draw buffer state.

BUG=703508

Change-Id: I7db5443141c65a3f9c638f07ba90f78d76e4e7b4
Reviewed-on: https://chromium-review.googlesource.com/457524
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>