libvncserver: integer overflow in vcSetXCutTextProc in VNConsole.c

An issue was discovered in vcSetXCutTextProc() in VNConsole.c in LinuxVNC and VNCommand from the LibVNC/vncterm distribution through 0.9.10. Missing sanitization of the client-specified message length may cause integer overflow or possibly have unspecified other impact via a specially crafted VNC packet.