Fix segfault when service is not found.
Fix segfault when service is not found.

Change-Id: Ibd79fca08771d2c63eb0963a4a95776813f78d67
Reviewed-on: http://gerrit.aldebaran.lan:8080/3092
Reviewed-by: llec <42f1a1c02cacc0f5b0188f0127ea77bedfdcf21a@aldebaran-robotics.com>
Tested-by: llec <42f1a1c02cacc0f5b0188f0127ea77bedfdcf21a@aldebaran-robotics.com>

bsautron/libqi,aldebaran/libqi,aldebaran/libqi,aldebaran/libqi-java,aldebaran/libqi-java,vbarbaresi/libqi,aldebaran/libqi,aldebaran/libqi-java