MediaBrowserServiceCompat: Fix NullPointerException

If a MediaBrowserServiceCompat does not call setSessionToken() in its
onCreate(), NPE occurs whenever a browser tries connecting to it.
This CL fixes the problem by adding a null check.

Bug: 38422762
Test: Passed MediaBrowserServiceCompatTest on API 19-25
Change-Id: I89dbbc4755ba2a72387e98941ba61919896dcde4
Merged-In: b3d603228afae9aaedca02554176ffff277cfd3b
4 files changed