Signature::isConvertibleTo: Fix a lolbug, it never worked and returned true always.
Signature::isConvertibleTo: Fix a lolbug, it never worked and returned true always.

Change-Id: I93ae42a1b36d175311b940af0baf9a4e3b61f83a
Reviewed-on: http://gerrit.aldebaran.lan:8080/7221
Reviewed-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>
Tested-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>

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