patch 8.1.1922: in diff mode global operations can be very slow

Problem:    In diff mode global operations can be very slow.
Solution:   Do not call diff_redraw() many times, call it once when redrawing.
            And also don't update folds multiple times.

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1922,
 /**/
     1921,
 /**/