Returning or yielding from a closureiter must restore "external"
exception, but `popCurrentException` from `blockLeaveActions` was
getting in the way. So now `blockLeaveActions` doesn't emit
`popCurrentException` for returns in closureiters. I'm not a fan of this
"abstraction leakage", but don't see a better solution yet. Any input is
much appreciated.
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Co-authored-by: Andreas Rumpf <araq4k@proton.me>