[Autotest] User Preferences failed to be saved when drone set is disabled

This CL fixed the bug when saving User Preferences failed due to drone set is
disabled.

BUG=chromium:242317
TEST=tested in local workstation
DEPLOY=afe

Change-Id: I23facc9c461930397357caec1549e649ee6ffc7f
Reviewed-on: https://gerrit.chromium.org/gerrit/58569
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
1 file changed