Fix SF bug # 1030941. In _parsegen(), in the clause where we're

Fix SF bug # 1030941.  In _parsegen(), in the clause where we're
capturing_preamble but we found a StartBoundaryNotFoundDefect, we need to
consume all lines from the current position to the EOF, which we'll set as the
epilogue of the current message.  If we're not at EOF when we return from
here, the outer message's capturing_preamble assertion will fail.