vim-patch:8.2.5163: crash when deleting buffers in diff mode

Problem:    Crash when deleting buffers in diff mode.
Solution:   Recompute diffs later.  Skip window without a valid buffer.
cd38bb4d83

src/nvim/diff.c

@@ -115,7 +115,10 @@ void diff_buf_delete(buf_T *buf)
       tp->tp_diff_invalid = true;
 
       if (tp == curtab) {
-        diff_redraw(true);
+        // don't redraw right away, more might change or buffer state
+        // is invalid right now
+        need_diff_redraw = true;
+        redraw_later(curwin, VALID);
       }
     }
   }
@@ -648,7 +651,8 @@ void diff_redraw(bool dofold)
 
   need_diff_redraw = false;
   FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-    if (!wp->w_p_diff) {
+    // when closing windows or wiping buffers skip invalid window
+    if (!wp->w_p_diff || !buf_valid(wp->w_buffer)) {
       continue;
     }
     redraw_later(wp, SOME_VALID);

src/nvim/testdir/test_diffmode.vim

@@ -1446,5 +1446,17 @@ func Test_diff_scroll()
   call delete('Xright')
 endfunc
 
+" This was trying to update diffs for a buffer being closed
+func Test_diff_only()
+  silent! lfile
+  set diff
+  lopen
+  norm o
+  silent! norm o
+
+  set nodiff
+  %bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab