expand: stops when one of given files doesn't exist

[cakebaker]

GNU expand shows an error message when a file doesn't exist and continues work with the next given arguments, while uutils expand stops when an error occurs.

GNU expand:

$ echo "a" > a
$ expand a nonexisting a
a
expand: nonexisting: No such file or directory
a
$ echo $?
1

uutils expand:

$ echo "a" > a
$ cargo run expand a nonexisting a
a
expand: nonexisting: No such file or directory
$ echo $?
1

This issue is very similar to #5809