tdf#120777 KDE5: Prohibit resizing windows unless they're marked resizeable

Change-Id: I412c3d263881d24dea1bb61520c2291d8f0b9b20
Reviewed-on: https://gerrit.libreoffice.org/63016
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>
Tested-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>
diff --git a/vcl/qt5/Qt5Frame.cxx b/vcl/qt5/Qt5Frame.cxx
index b5680b6..70c3de1 100644
--- a/vcl/qt5/Qt5Frame.cxx
+++ b/vcl/qt5/Qt5Frame.cxx
@@ -400,10 +400,12 @@
        m_bDefaultSize = false;
        if (isChild(false) || !m_pQWidget->isMaximized())
        {
            if (m_pTopLevel)
                m_pTopLevel->resize(nWidth, nHeight);
            QWidget* const pWidget = (m_pTopLevel) ? m_pTopLevel : m_pQWidget;

            if (m_nStyle & SalFrameStyleFlags::SIZEABLE)
                pWidget->resize(nWidth, nHeight);
            else
                m_pQWidget->resize(nWidth, nHeight);
                pWidget->setFixedSize(nWidth, nHeight);
        }
    }
    else if (m_bDefaultSize)