wayland: Don't set cursor surface scale when we don't have a surface

wayland: Don't set cursor surface scale when we don't have a surface

The setting of the the surface scale even when the surface is not
created from a surface was introduced due to a crash when getting the
buffers when dividing by the scale. The only reason I can see this is
that we get the buffer from a non-existing surface when the wl_cursor
has not yet been set.

Instead, use the name field to avoid trying to use the non-existing
surface, effectively avoiding the division-by-zero that way.

https://bugzilla.gnome.org/show_bug.cgi?id=746141