log: Fix when argument is an undefined static const class member.
log: Fix when argument is an undefined static const class member.

Change-Id: I76091ec90fd71ba00c500ca91a08f9b44d33970f
Reviewed-on: http://gerrit.aldebaran.lan:8080/12817
Reviewed-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>
Reviewed-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>
Tested-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>

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