The attached patch fixes a bug in libxcb-icccm that affects xcb-based WMs.
For example, with i3 window manager from ports/x11/i3, launching xev makes
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Core was generated by `i3'.
Program terminated with signal 8, Arithmetic exception.
#0 0x0a2f493a in xcb_get_wm_hints_from_reply (hints=0xcfbf9870,
reply=0x85607bc0) at /usr/xenocara/dist/xcb-util/icccm/icccm.c:639
639 num_elem = length / (reply->format / 8);