GVP::destroy: reset the value to 0
GVP::destroy: reset the value to 0

Change-Id: I6f7734f9814fe8c4a28436986c584eac55b8c310
Reviewed-on: http://gerrit.aldebaran.lan:8080/13202
Reviewed-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>
Tested-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>

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