Properly guard access to CloseGuard in finalizers.

CloseGuard instances are allocated in constructors and usually
assigned to final fields. This implies they're non-null in finalizers
except in the case where the constructor throws. We add a null check
to make sure we can continue cleaning up other state in the finalizer
(if applicable).

Also, this change decouples closeguard warnings in constructors
from other state based logic. This because the logic there is usually
duplicated with the call to close().

NOTE: This change is not a "complete" fix. Many of these finalizers
are broken in the case where <init> throws. The only objective of
this change is to make such errors more obvious.

Note that some of these classes don't have CTS tests.

Test: make, CtsMediaTestCases.
Bug: 35609098

Change-Id: I24d9e0215f80e44914dba8ab99b6312fd6ed1fc0