Framebuffer update of cursor-modified regions are sent even if client did not request them

[bk138]

https://github.com/LibVNC/libvncserver/blob/a06711e7fa9e47927007782cc9fe74e08313d1aa/src/libvncserver/cursor.c#L716 OR's the cursor region with the updateRegion in rfbSendFramebufferUpdate() which gets sent no matter what cl->requestedRegion is.

Spotted with SetUpdateRect() using {0,0,0,0} from 0e72da16493f0b994f9bb1277093608b869f53e4