fix bug with n > 2 images occurring when the height map on some tile is empty
fix bug with n > 2 images occurring when the height map on some tile is empty

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