VimHTML can double-encode UTF-8 when input is already decoded Perl text #2

I ran into a UTF-8 handling issue in Pod::Elemental::Transformer::VimHTML when highlighted input arrives as already-decoded Perl text.

In the failing case, content like guillemets in #!vim perl blocks can render as mojibake, for example «...» instead of «...».

The downstream fix that worked for me was:

• normalize likely double-encoded-looking decoded input before passing it to Text::VimColor
• avoid pre-encoding already-decoded Perl strings to octets
• only decode HTML output if it is not already flagged as UTF-8
• add an explicit use Carp qw(confess); import while touching the module

Downstream context:

• Perl Advent PR: Fix UTF-8 mojibake in #!vim highlighted blocks perladvent/Perl-Advent#663
• Companion fork PR carrying the module change: Add VimHTML transformer with UTF-8 handling fix perladvent/Pod-Elemental-Transformer-SynHi#3

If helpful, I can also put together a cleaner upstream-oriented PR from a fresh branch/repo shape. I wanted to at least report the bug and the working fix path first.