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.
diff --git a/src/diff.c b/src/diff.c
index df3dea0..eddf331 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -119,7 +119,12 @@
 	    tp->tp_diffbuf[i] = NULL;
 	    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(VALID);
+	    }
 	}
     }
 }
@@ -670,7 +675,8 @@
 
     need_diff_redraw = FALSE;
     FOR_ALL_WINDOWS(wp)
-	if (wp->w_p_diff)
+	// when closing windows or wiping buffers skip invalid window
+	if (wp->w_p_diff && buf_valid(wp->w_buffer))
 	{
 	    redraw_win_later(wp, SOME_VALID);
 	    if (wp != curwin)