[patch] DiffUpdated event is not triggered on the first or last window.

[h_east]

Hi Bram and developers,

How to reproduce:
- Prepare following Vim script file named `test.vim`.
  func Prepare_diffthis()
    au DiffUpdated * echomsg expand("<afile>")

    let bufnames = map(range(1,4), '"buf_" . v:val')
    for bn in bufnames
        let cmd = (bn[-1:] == "1") ? "edit" : "rightbelow vnew"
        exec cmd bn
        call setline(1, "Contents of " . bn)
    endfor
  endfunc

- Start vanilla Vim with the script above.
  $ vim --clean -S test.vim
- Execute function
  :call Prepare_diffthis()
- Perform `diffthis` for all windows.
  :windo diffthis

Expected behavior (I think):
- DiffUpdated is triggered for all windows.
  buf_1
  buf_2
  buf_3
  buf_4

Actual behavior:
- DiffUpdated is not triggered for the first window.  (Message `buf_1` is not 
displayed)
  buf_2
  buf_3
  buf_4


Continue to do the following command:
  :windo diffoff

Expected behavior (I think):
- DiffUpdated is triggered for all windows.
  buf_1
  buf_2
  buf_3
  buf_4

Actual behavior:
- DiffUpdated is not triggered for the last window.  (Message `buf_4` is not 
displayed)
  buf_1
  buf_2
  buf_3


A Patch attached.
Please check it.
There may be room for discussion about judgment conditions :)

--
Best regards,
Hirohito Higashi (h_east)

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diff --git a/src/diff.c b/src/diff.c
index 336157c6d..ab9992eab 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -941,7 +941,7 @@ ex_diffupdate(exarg_T *eap)	// "eap" can be NULL
 theend:
     // A redraw is needed if there were diffs and they were cleared, or there
     // are diffs now, which means they got updated.
-    if (had_diffs || curtab->tp_first_diff != NULL)
+    if (had_diffs || curtab->tp_first_diff != NULL || curwin->w_p_diff_saved)
     {
 	diff_redraw(TRUE);
 	apply_autocmds(EVENT_DIFFUPDATED, NULL, NULL, FALSE, curbuf);
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 5a3a6beee..5794fc4f0 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -32,7 +32,7 @@ func Test_diff_fold_sync()
   call win_gotoid(winone)
   call assert_equal(23, getcurpos()[1])
 
-  call assert_equal(1, g:update_count)
+  call assert_equal(2, g:update_count)
   au! DiffUpdated
 
   windo diffoff
@@ -924,3 +924,23 @@ func Test_diff_of_diff()
   call StopVimInTerminal(buf)
   call delete('Xtest_diff_diff')
 endfunc
+
+func Test_diff_diffupdated_target()
+  enew!
+  let g:update_target = []
+  au DiffUpdated * call add(g:update_target, expand("<afile>"))
+
+  let bufnames = map(range(1,4), '"buf_" . v:val')
+  for bn in bufnames
+      let cmd = (bn[-1:] == "1") ? "edit" : "rightbelow vnew"
+      exec cmd bn
+      call setline(1, "Contents of " . bn)
+  endfor
+  windo diffthis
+  call assert_equal(bufnames, g:update_target)
+
+  let g:update_target = []
+  windo diffoff
+  call assert_equal(bufnames, g:update_target)
+  au! DiffUpdated
+endfunc