[Issue 20489] Installer deleting files after install

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20489

--- Comment #6 from Simen Kjaeraas <simen.kjaras at gmail.com> ---
Out of 15 attempts, I've managed to get a borked install once. That's even
stranger, so I'm prepared to call it a fluke and say the fix works - at the
very least the incidence rate is a lot lower.

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