Segfault when constructing a HomogenousMesh from another HomogenousMesh

[rdeits]

In julia v0.6-rc2 on OSX, using GeometryTypes master (plus the fix from #91), the following code segfaults:

using MeshIO, GeometryTypes
using GeometryTypes: isvoid

VT = vertextype(GLNormalMesh)
FT = facetype(GLNormalMesh)
vs = [VT(0., 0, 0), VT(1., 0, 0), VT(0., 1, 0)]
fs = [FT(1, 2, 3)]

m = HomogenousMesh(vs, fs)
HomogenousMesh(m)

I haven't been able to figure out why.