vim-patch:8.1.0053 use typval_T in the caller of call_vim_function

Problem:	unreliable types for complete function arguments
Solution:	fix argument type for functions w/ unreliable type conversion(Ozaki Kiichi)
vim/vim#2993

src/nvim/testdir/test_ins_complete.vim

@@ -250,6 +250,31 @@ func Test_omni_dash()
   set omnifunc=
 endfunc
 
+func Test_completefunc_args()
+  let s:args = []
+  func! CompleteFunc(findstart, base)
+    let s:args += [[a:findstart, empty(a:base)]]
+  endfunc
+  new
+
+  set completefunc=CompleteFunc
+  call feedkeys("i\<C-X>\<C-U>\<Esc>", 'x')
+  call assert_equal([1, 1], s:args[0])
+  call assert_equal(0, s:args[1][0])
+  set completefunc=
+
+  let s:args = []
+  set omnifunc=CompleteFunc
+  call feedkeys("i\<C-X>\<C-O>\<Esc>", 'x')
+  call assert_equal([1, 1], s:args[0])
+  call assert_equal(0, s:args[1][0])
+  set omnifunc=
+
+  bwipe!
+  unlet s:args
+  delfunc CompleteFunc
+endfunc
+
 " Check that when using feedkeys() typeahead does not interrupt searching for
 " completions.
 func Test_compl_feedkeys()