pasting into ppc64 serial console kills qemu

- run qemu-system-ppc64
- when X window appears press Ctrl+Alt+3
- paste any text longer than 16 characters


qemu-system-ppc64: /home/abuild/rpmbuild/BUILD/qemu-2.6.1/hw/char/spapr_vty.c:40: vty_receive: Assertion `(dev->in - dev->out) < 16' failed.
Aborted (core dumped)

Broken in SUSE Leap 42.2 and git 4eb28abd52d48657cff6ff45e8dbbbefe4dbb414