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()

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/dumps/Test_crash_01.dump b/src/testdir/dumps/Test_crash_01.dump
new file mode 100644
index 0000000..1f0fd44
--- /dev/null
+++ b/src/testdir/dumps/Test_crash_01.dump
@@ -0,0 +1,20 @@
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