[DEBUG](iOS) libARDiscovery: Test if NetService TXTRecordData is not nil
[DEBUG](iOS) libARDiscovery: Test if NetService TXTRecordData is not nil

If so, the method dictionaryFromTXTRecordData: used to raise an exception and crashes.

Change-Id: I3bdb17f8bd3ba013156f42dcf6a6ede3c6fd75a4
Reviewed-on: https://gerrit.parrot.biz/17906
Reviewed-by: Nicolas Brulez <c7b4d7ddc34318e865922d5ddc9ce680dfb1b14c@parrot.com>

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