Fix NPE

NPE happens when there is an orphaned session which we've
tried to prevent in all cases.

Log an error message if this situation happens.

Bug: 227342978
Test: atest CtsRootPackageInstallerHostTestCases
Change-Id: Ia21323926bd9db1a6f05461904deb45b4c3dd0bc
(cherry picked from commit 07e31dfb1efabc8110d64819f26a06e12a35e020)
Merged-In: Ia21323926bd9db1a6f05461904deb45b4c3dd0bc
1 file changed