pretty-print: do not fail when cat_files() tries to show a masked file

pretty-print: do not fail when cat_files() tries to show a masked file

Before 661b5bfd216e383ac7836261eea9671875e6709b, cat_files() does not
check if a file is regular. If the file is a symlink to /dev/null, then
cat_files() simply shows an empty contents for the file.
With the offending commit, as the CHASE_MUST_BE_REGULAR flag is set,
hence when we found a masked file, the function fails.

Fixes #40313.
Fixes regression caused by 661b5bfd216e383ac7836261eea9671875e6709b.

Co-authored-by: gvenugo3 <gvenugo3@asu.edu>