fix(_minimal): fall back to defaults instead of _filedir

We don't actually know if filenames are wanted here, so there's no
reason to insist filename completions specifically. Besides, the bash
and readline defaults handle the basic filename completions at least as
well as `_filedir` does. They additionally make wildcard completions work.

Remove no longer needed long option splitting, as it is no longer needed
after this change.

Closes #444

Co-authored-by: Koichi Murase <myoga.murase@gmail.com>

Author: scop

bash_completion

@@ -2487,10 +2487,9 @@ unset -f _install_xspec
 # Minimal completion to use as fallback in _completion_loader.
 _minimal()
 {
-    local cur prev words cword split comp_args
-    _comp_initialize -s -- "$@" || return
-    $split && return
-    _filedir
+    local cur prev words cword comp_args
+    _comp_initialize -- "$@" || return
+    compopt -o bashdefault -o default
 }
 # Complete the empty string to allow completion of '>', '>>', and '<' on < 4.3
 # https://lists.gnu.org/archive/html/bug-bash/2012-01/msg00045.html