Fix typo in dmd.expression apparently causing sporadic frontend crashes

[kinke]

Seems to fix sporadic segfaults reported in https://issues.dlang.org/show_bug.cgi?id=18864.

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[kinke]

That was quick, thanks; I should have targeted stable though. :/ Pinging @MartinNowak.

[wilzbach]

Ah we typically only do cherry-picking if it's important, so if you feel like this really should be part of 2.080.1, simply cherry-pick and open a new PR.
OTOH the next release will be in one month.

[kinke]

@wilzbach: So a fix for random DMD segfaults isn't important enough to be cherry-picked by one of you guys? What is then? ;)

[dnadlinger]

Sorry about that – I was on my phone, and the mobile version doesn't display the target branch, so I didn't notice.

[wilzbach]

Ehm I'm currently traveling and without laptop, otherwise I would have opened the cherry-pick for you.
Well, Martin always complains about this because these cherry-picks can result in ugly merge conflicts, so yep we often don't bother except for really important things :/

[WalterBright]

This PR was a bug fix for https://issues.dlang.org/show_bug.cgi?id=18864