Fix setting of std::optional variables.

Technically, this doesn't matter since the bug always causes the
unwind to happen on the current thread, and the current thread
is the one that is crashing. However, if that ever changed, the
old code would unwind the wrong thread.

Bug: 120606663

Tag: #stability

Test: Manual - Ran bluetooth_stack_with_facade on device and
Test: crashed on a non-main thread and got a good unwind.
Test: Manual - Ran root_canal on host and crashed on a non-main
Test: thread and got a good unwind.
Change-Id: Idd691b4de0cfc37cde7344b69b2cd4e2f0ee8729