rfb: Fix inheritance in CMsgWriter

rfb: Fix inheritance in CMsgWriter

InputHandler declares the second parameter of clientCutText
as an int.

Fixes:

/home/shade/dev/tigervnc/common/rfb/CMsgWriter.h:60:18: error: 'rfb::CMsgWriter::clientCutText' hides overloaded virtual function [-Werror,-Woverloaded-virtual]
    virtual void clientCutText(const char* str, rdr::U32 len);
                 ^
/home/shade/dev/tigervnc/common/rfb/InputHandler.h:36:18: note: hidden overloaded virtual function 'rfb::InputHandler::clientCutText' declared here: type mismatch at 2nd parameter ('int' vs 'rdr::U32' (aka 'unsigned int'))
    virtual void clientCutText(const char* str, int len) {}
                 ^