patch 8.2.3920: restoring directory after using another window is inefficient

Problem:    Restoring directory after using another window is inefficient.
Solution:   Only restore the directory for win_execute().  Apply 'autochdir'
            only when needed.
diff --git a/src/version.c b/src/version.c
index 2045de9..8963062 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3920,
+/**/
     3919,
 /**/
     3918,