Sine fill doesn't work on meshes

Repro:
1. Open `Patterns/CellularAutomata/hex_B2oS2m34_gliders.vtu` in Ready, change number of chemicals to 4, Save Compact... as `hex_packet.vtu`
2. Overwrite the `<RD>` section in `hex_packet.vtu` with the one from `Patterns/Schrodinger1926/packet_reflect2D.vti`.
3. Open `hex_packet.vtu` in Ready. Note that chemicals `a` and `b` are blank.