Skip syncing if image_dir does not exist

Devserver should assume no image exists if image_dir is not
found.

This was CL:183543, which was committed but later got lost in the
rebase of other CLs.

BUG=chromium:337533
TEST=None

Change-Id: I4c06a2661bd5200108e6fe487bb87d3cfd7793ec
Reviewed-on: https://chromium-review.googlesource.com/195214
Tested-by: Yu-Ju Hong <yjhong@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Yu-Ju Hong <yjhong@chromium.org>
1 file changed