Entering invalid VNC port in VM editor doesn't inform user until they start the VM

If I manually set the VNC port for a VM, and enter 5717 (for example) the form accepts it. I don't find out that VNC ports must be 5900 or greater until I try to start the VM, meaning I then have to go back into the editor and change it again.

If the port number entered is invalid, that should be shown in the editor (inline, not as a modal alert!) as soon as the focus leaves the port number field.