Panic on a -current from 13/12/2018

[Chavdar Ivanov]

Hi,

On 8.99.27 AMD64 running under VirtualBox I got this morning the panic
in http://ci4ic4.tx0.org/ci4ic4-panic-01.png

I have the  coredump, if it is of interest. I thought it might be
useful, as it is apparently in the wm driver.

Chavdar
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