-Dmad minitest failure bisect

-Dmad minitest failure bisect

Tony Cook wrote:
>Smokes with -Dmad have been failing during make minitest since the
>middle of last month.

Mostly fixed by the attached patch.  The fault is a logic error on my
part, probably from the early phase of developing the lexer API patch,
when I didn't properly understand the various buffer pointer variables.

In my tests with -Dmad, I'm still getting a test failure ("panic: input
overflow") from t/op/incfilter.t.  The underlying problem is the filter
layer mishandling things when a filter function gives it a multiline
string, so it generates an invalid SV state (strlen(SvPVX(PL_linestr))
> SvCUR(PL_linestr)).  This faulty state also occurs without -Dmad,
and so doesn't appear to be Mad-related, it just doesn't in practice
cause the test panic without -Dmad.  I'm investigating this bug now.

-zefram

Signed-off-by: H.Merijn Brand <h.m.brand@xs4all.nl>