Problem:
The cmdpreview saved undo nodes on cmdpreview_prepare() from ex_getln.c may
become invalid (free) if the preview function makes undo operations, causing
heap-use-after-free errors.
Solution:
Save the buffer undo list on cmdpreview_prepare)_ and start a new empty one. On
cmdpreview_restore_state(), undo all the entries in the new undo list and
restore the original one. With this approach, the preview function will be
allowed to undo only its own changes.
Fix#20036Fix#20248
643bea31b8