bug#59803: completion-at-point in shell buffer ignores some files

[Nicolas Graner]

In a *Shell* buffer, file name completion ignores file names already
present on the current line. For example, if you have a file named `foo'
and no other file starting with an f, when you type:

$ cp f<TAB> f<TAB>

the first <TAB> completes `f' to `foo', but the second <TAB> gives a `No
match' error.

Similarly, if you have files named foo1, foo2, foo3 and foo4, then:

$ mv foo1 foo2 f<TAB>

shows only foo3 and foo4 in the completions buffer.

Happens in emacs 29 but not in 28.

Nicolas