Return invalid task id if no acceptable target app

No matter the app is not found or has different uid, return
the invalid id to indicate that the add operation is failed.
So the caller won't know whether the specified package exists
or not.

Bug: 189122913
Test: Pass intent with specified component name to
      ActivityManager#addAppTask.
Change-Id: I013264414c60f2d9864a5fcc369180425f20529e