Update htmlify.p6 to fix 'got empty filename' issue #1971.  Was looking for "infix C<foo>" and tried to process '=head1 baz X<|baz>' same way which results in empty document name.  Note 'infix X<C<foo>>' is sometimes used so need to check content as well as .type eq 'X'.
Update htmlify.p6 to fix 'got empty filename' issue #1971.  Was looking
for "infix C<foo>" and tried to process '=head1 baz X<|baz>' same way
which results in empty document name.  Note 'infix X<C<foo>>' is sometimes
used so need to check content as well as .type eq 'X'.

stmuk/doc,stmuk/doc,dmaestro/doc,MasterDuke17/doc,jonathanstowe/doc,stmuk/doc,tbrowder/doc,tbrowder/doc,MasterDuke17/doc,jonathanstowe/doc,jonathanstowe/doc,jonathanstowe/doc,stmuk/doc,dmaestro/doc,stmuk/doc,dmaestro/doc,perl6/doc,jonathanstowe/doc,MasterDuke17/doc,dmaestro/doc,perl6/doc,perl6/doc,perl6/doc,perl6/doc,tbrowder/doc,tbrowder/doc,dmaestro/doc,MasterDuke17/doc