libbanshee: Fix crash on g_free when look for subtile description
libbanshee: Fix crash on g_free when look for subtile description

This crash appear on gstreamer version before 0.10.24 because code are
not always setup and it was not initialise to null so it can
contain random memory which lead to crash.
A small mem leak was fixed too in same function.

arfbtwn/banshee,Dynalon/banshee-osx,ixfalia/banshee,ixfalia/banshee,GNOME/banshee,GNOME/banshee,Carbenium/banshee,dufoli/banshee,dufoli/banshee,Dynalon/banshee-osx,babycaseny/banshee,arfbtwn/banshee,GNOME/banshee,Dynalon/banshee-osx,babycaseny/banshee,GNOME/banshee,arfbtwn/banshee,arfbtwn/banshee,GNOME/banshee,ixfalia/banshee,arfbtwn/banshee,stsundermann/banshee,dufoli/banshee,arfbtwn/banshee,Dynalon/banshee-osx,ixfalia/banshee,stsundermann/banshee,ixfalia/banshee,arfbtwn/banshee,arfbtwn/banshee,Carbenium/banshee,dufoli/banshee,Dynalon/banshee-osx,GNOME/banshee,GNOME/banshee,Dynalon/banshee-osx,babycaseny/banshee,babycaseny/banshee,babycaseny/banshee,Carbenium/banshee,dufoli/banshee,ixfalia/banshee,babycaseny/banshee,stsundermann/banshee,Carbenium/banshee,GNOME/banshee,Carbenium/banshee,Dynalon/banshee-osx,stsundermann/banshee,stsundermann/banshee,dufoli/banshee,ixfalia/banshee,babycaseny/banshee,babycaseny/banshee,stsundermann/banshee,Carbenium/banshee,dufoli/banshee,stsundermann/banshee,Dynalon/banshee-osx,dufoli/banshee,ixfalia/banshee,stsundermann/banshee