[Issue 15586] std.utf.toUTF8() segfaults when fed an invalid dchar

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15586

--- Comment #6 from thomas.bockman at gmail.com ---
I may have reduced this one too far:
   
https://github.com/D-Programming-Language/phobos/pull/3943#issuecomment-173381348

Arguably, the real bug is that certain other functions in Phobos call
`toUTF8()` without verifying that the input they are supplying satisfies the
contract. This will be a bit more work to fix, though.

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