Pass empty list to setqflist when setting attrs

The list argument is ignored if the 'what' argument is present, and
recently vim has started throwing and error if they are both present and
the list is not empty.

Fixes mhinz#231

Author: mvanderkamp

plugin/grepper.vim

@@ -984,9 +984,9 @@ function! s:finish_up(flags)
           \ ? cmdline
           \ : {'title': cmdline, 'context': {'query': @/}}
     if qf
-      call setqflist(list, a:flags.append ? 'a' : 'r', attrs)
+      call setqflist([], a:flags.append ? 'a' : 'r', attrs)
     else
-      call setloclist(0, list, a:flags.append ? 'a' : 'r', attrs)
+      call setloclist(0, [], a:flags.append ? 'a' : 'r', attrs)
     endif
   catch /E118/
   endtry