In a previous step of the mesh writing process, the loop `totlayer` was
replaced and a temporary vector is used for layer data instead. Use this
temporary vector to find the UV sub-layers, since the vector and the
CustomData struct in the mesh don't necessarily match. Also use a
local variable for mesh loop count to make it clearer that the mesh
isn't used except at the end.
Thanks to Campbell for finding the source of this error.
Hans Goudey
de49d18af5