Test bug_686.py: Unlock mutex after use
Test bug_686.py: Unlock mutex after use

Fix warning:
QMutex: destroying locked mutex

Change-Id: If19294847610cad27c7c6a440aee65bf8723d9c0
Reviewed-by: Christian Tismer <3f32342346a37828fd9c8841ea4579d28b46cf08@stackless.com>

qtproject/pyside-pyside,qtproject/pyside-pyside,qtproject/pyside-pyside,qtproject/pyside-pyside,qtproject/pyside-pyside