When extracting UV point indices, only the vertex points coming from the
original geometry should be drawn. For this, the routines (for subdivision
and coarse meshes) would only consider a vertex to be real if the extraction
type is `MAPPED`, and that an origin index layer on the vertices exist
with a valid origin index for the current vertex.
However, if the extraction type is `MESH`, which can happen with for
example an empty Geometry Node modifier, or with deferred subdivision,
this would consider every vertex to not be "real" and therefore hidden from
the UV editor.
This reworks the condition for "realness" to also consider a vertex to be
real if there is no origin layer on the vertices. The check on the extraction
type is removed as it becomes redundant.
This only modifies the check in the UV data extraction for point indices,
however similar checks exist throughout the extraction code, these will
be dealt with separately in master.
Differential Revision: https://developer.blender.org/D14773
fa9e878e79