patch 9.0.1873: [security] heap-buffer-overflow in vim_regsub_both

Problem:  heap-buffer-overflow in vim_regsub_both
Solution: Disallow exchanging windows when textlock is active

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/window.c b/src/window.c
index 1af2395..f77ede3 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1733,6 +1733,11 @@
 	beep_flush();
 	return;
     }
+    if (text_or_buf_locked())
+    {
+	beep_flush();
+	return;
+    }
 
 #ifdef FEAT_GUI
     need_mouse_correct = TRUE;