patch 8.1.0253: saving and restoring window title does not always work

Problem:    Saving and restoring window title does not always work.
Solution:   Use the stack push and pop commands. (Kouichi Iwamoto,
            closes #3059)
diff --git a/src/os_mswin.c b/src/os_mswin.c
index 5dbfd0e..2112b0c 100644
--- a/src/os_mswin.c
+++ b/src/os_mswin.c
@@ -304,9 +304,9 @@
 /*
  * Restore the window/icon title.
  * which is one of:
- *  1: Just restore title
- *  2: Just restore icon (which we don't have)
- *  3: Restore title and icon (which we don't have)
+ *  SAVE_RESTORE_TITLE: Just restore title
+ *  SAVE_RESTORE_ICON:  Just restore icon (which we don't have)
+ *  SAVE_RESTORE_BOTH:  Restore title and icon (which we don't have)
  */
     void
 mch_restore_title(int which UNUSED)