QEMU no longer allows to use full TCP port range for VNC

After upgrade to QEMU version 2.1.0 (Debian 2.1+dfsg-4ubuntu6), I am no longer able to use any TCP port for VNC display.
For example, if I need to assign VNC server a TCP port 443, I used to run:
# qemu-system-x86_64 -vnc :-5457
qemu-system-x86_64: Failed to start VNC server on `:-1000': can't convert to a number:-5457
expected behavior: as any VNC software, take port base of 5900, substract 5457 display number, and use TCP port 443

I ask to change vnc port conversion routine to allow input values in range of all TCP ports, from 1 to 65535.

I really depend on ability to use full TCP range for VNC port numbers, and inablity to do so in new version of QEMU is very disappointing.