Test for null package in isEnabledAndMatches()

Bug: 188174037

Avoid an NPE is isEnabledAndMatches() by returning false if no package
is found matching the component name.

This does not address the more general problem uncovered by the bug,
which is that a thread that has multiple calls into PM on the stack
might end up executing with different snapshots.

Test: atest
 * CtsContentTestCases
Change-Id: Ib4e929a62edf3393e0177f5d85c9b3fe1e0697d8