Qt: Make buildbot happy

capture_interfaces_dialog.cpp: In member function ‘void CaptureInterfacesDialog::updateStatistics()’:
capture_interfaces_dialog.cpp:483:100: error: operation on ‘points’ may be undefined [-Werror=sequence-point]
             QList<int> *points = points = ti->data(col_traffic_, Qt::UserRole).value<QList<int> *>();

Change-Id: I63afb0f207142d516403968f6a3e988f8ad61d4d
Reviewed-on: https://code.wireshark.org/review/3491
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>