This could happen when linking a program with missing attachments
and shaders that have no compiled sources.

Also re-enables the EGL program cache control tests, which were
disabled due to a wrong extension name check.

Bug: chromium:827158
Change-Id: I181f878093c6e3a4acc51552ade8e7c084733a3d
Reviewed-on: https://chromium-review.googlesource.com/989262Reviewed-by: Luc Ferron <lucferron@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>