Defined-or causes stringify / boolean overload call when run under Devel::Cover

[mohawk2]

As worked around in EntropyOrg/p5-Data-Frame@b3f456d, use of:

        return ( $self->_tie_hash // $self );

caused the stringify overload to be called, which in that context caused a problem. Switching it to:

        my $tmp = $self->_tie_hash; # avoid // as breaks Devel::Cover
        $tmp = $self if !defined $tmp;
        $tmp;

made the problem go away. On adding a confess to the stringify overload, the stack trace read:

t/traits.t ................. STACKTRACE at (dir)/blib/lib/Data/Frame.pm line 209.
        Data::Frame::string(Data::Frame__WITH__Data::Frame::Role::Rlike=HASH(0x6033b1751e00)) called at (dir)/blib/lib/Data/Frame.pm line 48
        Data::Frame::__ANON__(Data::Frame__WITH__Data::Frame::Role::Rlike=HASH(0x6033b1751e00), undef, "") called at (dir)/blib/lib/Data/Frame/Partial/Sugar.pm line 85
        Data::Frame::Partial::Sugar::__ANON__(Data::Frame__WITH__Data::Frame::Role::Rlike=HASH(0x6033b1751e00), undef, "") called at (eval 526)[(perlbrew)/libs/perl-5.32.0@normal/lib/perl5/Sub/Quote.pm:3] line 45
        Data::Frame__WITH__Data::Frame::Role::Rlike::new("Data::Frame__WITH__Data::Frame::Role::Rlike", "columns", ARRAY(0x6033b170ea00)) called at (eval 525)[(perlbrew)/libs/perl-5.32.0@normal/lib/perl5/Sub/Quote.pm:3] line 27
        Data::Frame::new("Data::Frame__WITH__Data::Frame::Role::Rlike", "columns", ARRAY(0x6033b170ea00)) called at t/traits.t line 12

so Sub::Quote may be part of the fun.