Implement tp_strdiff using g_strcmp0.
Implement tp_strdiff using g_strcmp0.

Clang's analyzer, like Coverity before it, isn't smart enough to realise
that the first two conditions between them guarantee that, if you get to
the end, left and right are non-NULL.

But the point is moot, since we can just use a Glib function.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib