[fix] fix compilation with --disable-webserver

While updating XBMC to current master on my gentoo box, I discovered this with USE="-webserver" (which translates to 'configure --disable-webserver'):

    CPP     xbmc/network/NetworkServices.o
    NetworkServices.cpp: In Konstruktor »CNetworkServices::CNetworkServices()«:
    NetworkServices.cpp:106:1: Fehler: expected identifier before »{« token

This rather simple fix makes it compile and produces a working binary with and without webserver.