Add missing mutex to qi::log HeadFileLogHandler
Add missing mutex to qi::log HeadFileLogHandler

Change-Id: I05f1ac48b12e64576caa5ed2fa9914d9ea5d8a3e
Reviewed-on: http://gerrit.aldebaran.lan:8080/11311
Reviewed-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>
Tested-by: llec <42f1a1c02cacc0f5b0188f0127ea77bedfdcf21a@aldebaran-robotics.com>

bsautron/libqi,aldebaran/libqi,vbarbaresi/libqi,aldebaran/libqi,aldebaran/libqi