Bug#884648: mate-panel occasionally crashes with segfault

[agafnd at openmailbox.org]

Something that might be interesting to note: I've had the "compositing
window manager" option turned on, and had the panels at around 28%
transparency. I've since turned both things off (due to my experiments
related to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=884116).

Since I don't know how the crash is triggered, I don't know whether this
helps or not. I haven't had it happen yet, but I've previously gone quite
a while without a crash.

Regards, Agafnd