Make sure to mutex around job-set iteration

If something mucks with the job set while we're iterating through
it, we're going to have a bad day.

Change-Id: I2e5603f4dd025b2e1819c7e84d59882bad98ae7a
Fixes: 72105511
Test: atest CtsJobSchedulerTestCases
Test: atest FrameworksServicesTests:com.android.server.job.BackgroundRestrictionsTest
1 file changed