Signature visitor: return static signature when list or map is empty
Signature visitor: return static signature when list or map is empty

Change-Id: I45d1e44b8e789d773875c42afc1b58d838fb604f
Reviewed-on: http://gerrit.aldebaran.lan/37074
Reviewed-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>
Tested-by: pdaouadi <fc1eb3334d3fdad315bae23aa166bc70bd434067@aldebaran-robotics.com>

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