Do _filedir in _command_offset only for commands with no completions installed.

If we have a completion installed for the actual command invoked via
sudo etc, it is very much possible and fine that no completions are
returned from it, and doing _filedir in these cases is not the right
thing to do.

bash_completion

@@ -1527,10 +1527,10 @@ _command_offset()
                 cspec=${cspec%%${cmd##*/}};
                 COMPREPLY=( $( eval compgen "$cspec" -- "$cur" ) );
             fi
+        elif [ ${#COMPREPLY[@]} -eq 0 ]; then
+            _filedir
         fi
     fi
-
-    [ ${#COMPREPLY[@]} -eq 0 ] && _filedir
 }
 complete -F _command aoss command do else eval exec ltrace nice nohup padsp \
     then time tsocks vsound xargs