devel/qt4-linguist: unbreak with clang 4.0

messagemodel.cpp:186:61: error: ordered comparison between pointer and zero ('MessageItem *' and 'int')

if (c->findMessage(m->text(), m->comment()) >= 0)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~

PR: 216051
Submitted by: Adriaan de Groot <groot@kde.org>
Obtained from: upstream (Qt5)
Approved by: kde (tcberner)
MFH: 2017Q1 (changes behavior)
Differential Revision: https://reviews.freebsd.org/D9184