[task scheduler] Another case for forgiving failure to read tasks.json
[task scheduler] Another case for forgiving failure to read tasks.json

BUG=skia:5723

Change-Id: I145b5af73ebeef195df6358e395b32be4ed8bec1
Reviewed-on: https://skia-review.googlesource.com/2996
Reviewed-by: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot