Optimization when looking up requests for release

Including an optimzation in handleReleaseNetworkRequest when
looking up a request so that in the chance an app shuts down prior to
the request being released, it doesn't cause errors when looking
validating that apps uid->package name.

Bug: 178729499
Test: atest FrameworksNetTests
atest ExtServicesUnitTests on CF and making sure no remote exceptions.

Change-Id: I2c49511a1385b47fba075b2794685ae2bc80abba