Using BindFramebuffer(1) then GenFramebuffers would return 1.
This leads to a memory leak and was something that was obscuring
debugging a bug in my ReadPixels fix for ES3.

This also fixes a bug where running the texture tests along produces
some random failures.

BUG=angleproject:1290
BUG=angleproject:1299

Change-Id: If11e8c743d2ddde725b12749ac012f670cd290e1
Reviewed-on: https://chromium-review.googlesource.com/324820Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>