[DEBUG] fix bug while reading pending rx data
[DEBUG] fix bug while reading pending rx data

First socket read result was not checked and negative value could be set to rxData.size which is unsigned

Change-Id: I157fcb8b0b0431bfec743d7a73ffbe2ac145d3e6
Reviewed-on: https://gerrit.parrot.biz/31628
Reviewed-by: Djavan Bertrand <7232792b712c7d1777e4e988572ac52f60124955@parrot.com>

Parrot-Developers/libARDiscovery,Parrot-Developers/libARDiscovery,Parrot-Developers/libARDiscovery,Parrot-Developers/libARDiscovery