Fix booting on arm64

[andrew]

Summary

Fix booting on some arm64 systems after r327879 by fixing the call to
utf8_to_ucs2 in boot1.efi. We need to initialise the ucs2 output string
so it will allocate space, and use the return value to determine if the
call was successful.

[imp]

stand/efi/boot1/boot1.c

93

Why isn't testing uv == NULL sufficient? We always don't change it when there's an error. The bug here is that uv wasn't initialized to NULL like efi_setenv_freebsd_wcs was.

109–111

We have the same code here.

[andrew]

stand/efi/boot1/boot1.c

93

It's allocated at the start of utf8_to_ucs2. I don't see where it's then set to NULL.

109–111

That also looks wrong, however as utf8_to_ucs2 only seems to fail when the input string is bad I think the error case in either function is unlikely.

[imp]

stand/efi/boot1/boot1.c

93

Yea, you're right.... Other code I've written sets it to null and I'd assumed this did too. It should, but doesn't, so this check is right.

109–111

We should do the same check here of the return value.

[imp]

See also https://reviews.freebsd.org/D13917, but I think checking the return values is better in both places.