fix(_comp_compgen_filedir_xspec): fix for empty "toks" and simplify

bash_completion

@@ -3051,15 +3051,11 @@ _comp_compgen_filedir_xspec()
 
     ((${#toks[@]})) || return 1
 
-    # Remove . and .. (as well as */. and */..) from suggestions,
-    # unless .. or */.. was typed explicitly by the user
-    # (for users who use tab-completion to append a slash after '..')
-    if [[ ${cur} != @(..|*/..) ]]; then
-        local i
-        for i in "${!toks[@]}"; do
-            [[ ${toks[$i]} == @(.|..|*/.|*/..) ]] &&
-                unset -v "toks[$i]"
-        done
+    # Remove . and .. (as well as */. and */..) from suggestions, unless .. or
+    # */.. was typed explicitly by the user (for users who use tab-completion
+    # to append a slash after '..')
+    if [[ $cur != ?(*/).. ]]; then
+        _comp_compgen -Rv toks -- -X '?(*/)@(.|..)' -W '"${toks[@]}"' || return 1
     fi
 
     compopt -o filenames