Fix bug in recently modified UDIM code (#1519)
Fix bug in recently modified UDIM code (#1519)

Forgot to recheck for broken file after changing UDIM name pattern into
a concrete file. A better solution is to fully recurse (just one level)
to perform all the initial checks on the concrete file.
OpenImageIO/oiio,lgritz/oiio,lgritz/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,lgritz/oiio