process_tile_pair doesn't need to return the path to the height map
process_tile_pair doesn't need to return the path to the height map

As the path is hardcoded, it's known in advance.
Checking if the tile is masked can be done once for all the pairs.

mnhrdt/s2p,dyoussef/s2p,carlodef/s2p,dyoussef/s2p,dyoussef/s2p,dyoussef/s2p,carlodef/s2p,jmichel-otb/s2p,jmichel-otb/s2p,MISS3D/s2p,MISS3D/s2p,jmichel-otb/s2p,MISS3D/s2p,jmichel-otb/s2p,mnhrdt/s2p,MISS3D/s2p