sv_vcatpvfn_flags: Use utf8_to_uv_or_die

[khwilliamson]

This is a change in behavior for malformed input. Previously it warned and substituted 0; the warnings remain, but now it substitutes the REPLACEMENT CHARACTER.

• This set of changes does not require a perldelta entry.

[tonycoz]

This is a change in behavior for malformed input. Previously it warned and substituted 0; the warnings remain, but now it substitutes the REPLACEMENT CHARACTER.

I'm confused, you're calling utf8_to_uv_or_die(), which croaks on a decoding failure, but the commit message says it produces a replacement character instead.

[khwilliamson]

It looks like I was the one who was confused. I hope it was just a copy paste error. Anyway, it doesn't return, but croaks in the face of malformed input. I'm now a bit reticent about doing this given that a couple of such commits had to be backed out. But I don't know that there is a decent recovery path forward here when this condition occurs. And there are already places in this function where it panics when it doesn't know how to go on

[tonycoz]

• This set of changes does not require a perldelta entry.

If this and other similar changes remain I do think we do need some sort of perldelta entry.

[khwilliamson]

I agree.