SharedRefBase: detect double-ownership

If the internal SharedRefBase weak_ptr is promotable while it is being
destroyed, this means that the SharedRefBase object is double-owned, and
something else deleted it. Add an explicit log for this case.

Fixes: 194905504
Test: libbinder_ndk_unit_test
Change-Id: Ib6aa09ff8e659e52eebe96c14d127a6e7c186cff