Make surface_gl_create_texture() idempotent: if the surface is already
bound to a texture, do not create a new one.

This fixes texture leaks when there are multiple DBus listeners, for
example.

Reported-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220214201337.1814787-3-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>