Fix removing empty trailing closure parentheses in a curried call

[a7medev]

Keep empty trailing closure parentheses in a curried call to avoid the compiler associating the trailing closure with the called expression (which is itself a call) breaking the code.

Fixes #1070

[a7medev]

@swift-ci please test

[a7medev]

@swift-ci please test

[allevato]

Looks good to me, thanks!

@bnbarham I saw your PR #1072 trying to deal with the older Windows toolchain issues; do you want to wait for that to resolve before we merge changes like this? (It seems fine, given that it passes everywhere else.)

[bnbarham]

I'm fine with merging, they're currently required but if you give me a ping I'll force merge it. I know what it is now, just need to find a way to workaround it.