Visualizer: Fix deadlock on close

Visualizer gets stuck in mCaptureThread::requestExitAndWait due to a
deadlock between mCaptureThread::mRunning and mCaptureLock.

Temporarily release mCaptureLock upon mCaptureThread::requestExitAndWait.

Test: Clarity -> Response, rapidly toggle visualizer enable, disable
Bug: 135326776
authored-by: Weiyin Jiang <wjiang@codeaurora.org>
Change-Id: If32431c4d7b271b7ea61168cb1a5a42f3a1cd66e