patch 9.0.0907: restoring window after WinScrolled may fail

Problem:    Restoring window after WinScrolled may fail.
Solution:   Lock the window layout when triggering WinScrolled.
diff --git a/src/errors.h b/src/errors.h
index 0f54eba..30032c0 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3341,3 +3341,5 @@
 #endif
 EXTERN char e_cannot_change_user_commands_while_listing[]
 	INIT(= N_("E1311: Cannot change user commands while listing"));
+EXTERN char e_not_allowed_to_change_window_layout_in_this_autocmd[]
+	INIT(= N_("E1312: Not allowed to change the window layout in this autocmd"));