graphics_utils.py: fix get_modetest_crtcs.

When a CRTC gets disabled the fb, and width/height are set to 0.
Lets skip over these.

BUG=chromium:544257
TEST=None.

Change-Id: Ida788b98eafa865e6d5a844641d1efdf0b319c3e
Reviewed-on: https://chromium-review.googlesource.com/317317
Commit-Ready: Ilja Friedel <ihf@chromium.org>
Tested-by: Ilja Friedel <ihf@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>
1 file changed