Set FBU.bytes to 1 in encHandlers.COPYRECT

FBU.bytes must be set before return false to indicate that the FBU
header has been read. If not set then "if (FBU.bytes == 0) { ..}"
in framebufferUpdate will be entered and the copyrect header will
be interpreted as a new FBU leading to a "unsupported encoding"
disconnect error.