vnc: vncviewer insufficient encoding value validation in CMsgReader::readRect

The CMsgReader::readRect function in the VNC Viewer component in RealVNC VNC Free Edition 4.0 through 4.1.2, Enterprise Edition E4.0 through E4.4.2, and Personal Edition P4.0 through P4.4.2 allows remote VNC servers to execute arbitrary code via crafted RFB protocol data, related to "encoding typ...