... instead of the nested MutexGuard and clear.
Really had to look twice, that the MutexGuard and ResettableGuard
use the same Mutex - who came up with this... yup myself.

Change-Id: I70326772a9be8352f169a26467529a7c4100a20d
Reviewed-on: https://gerrit.libreoffice.org/70385
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>