Make dexdump2 more forgiving on closing not-live register.

Rationale:
In order to match dexdump behavior more closely, we should
not log fatally when an already closed register is closed
again in a debug node. Such a not-live to not-live transition
is clearly redundant, but harmless to just ignore.

Test: test-art-host-dexdump
Bug: 38367835

Change-Id: Icf5397323c7197ccde0ce80caf8d952f44f65a3a