We were not checking for an invalid renderbuffer when attaching
to a framebuffer.

Change-Id: Ie29dca1833cc8c2b974f746d51dbee848f52a741
Reviewed-on: https://chromium-review.googlesource.com/181558Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>