Fix race condition in dumpDebug

The dumpDebug method was calling isImeSessionAvailableLocked to ensure
that mCurBindState was not null, but this was happening before
acquiring the lock. When acquiring the lock and reading the value, this
was now null due to an intermediary unbind operation which already had
the lock.

Test: none
Bug: 282815830
Change-Id: I0fddfb12c14eda109cc985eedadc9d3237dff8b0