vim-patch:9.0.1840: [security] use-after-free in do_ecmd

Problem:  use-after-free in do_ecmd
Solution: Verify oldwin pointer after reset_VIsual()

e1dc9a6275

N/A patches for version.c:
vim-patch:9.0.1841: style: trailing whitespace in ex_cmds.c

Co-authored-by: Christian Brabandt <cb@256bit.org>
(cherry picked from commit 2ffd8d98fa)

test/functional/legacy/crash_spec.lua

@@ -0,0 +1,16 @@
+local helpers = require('test.functional.helpers')(after_each)
+local assert_alive = helpers.assert_alive
+local clear = helpers.clear
+local command = helpers.command
+local feed = helpers.feed
+
+before_each(clear)
+
+-- oldtest: Test_crash1()
+it('no crash when ending Visual mode while editing buffer closes window', function()
+  command('new')
+  command('autocmd ModeChanged v:n ++once close')
+  feed('v')
+  command('enew')
+  assert_alive()
+end)