Fix ModelData pointer alignment;
Fix ModelData pointer alignment;

ModelData manages a single allocation and creates pointers into
that allocation.  These pointers were tightly packed, creating
alignment issues which triggered undefined behavior.  Now, the
pointers are all aligned to 8 byte boundaries.

bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr