qt59.qtvirtualkeyboard: fix CVE-2018-19865

CVE-2018-19865 tracks the issue of qtvirtualkeyboard where it logs all
user input. With this commit we are applying the recommended patches
form the upstream project.

More details can be obtained from the Qt annoucement [1].

[1] https://blog.qt.io/blog/2018/12/04/qt-5-11-3-released-important-security-updates/