neariso propagation can result in a 0-deep layer

[perlman]

Neariso propagation can result in a tier having a 0-depth voxel size which is silly. Should not go below 1.

neariso_imagesize values

"neariso_imagesize": { "0": [ 407040, 202240, 128 ], "1": [ 203520, 101120, 128 ], "2": [ 101760, 50560, 128 ], "3": [ 50880, 25280, 128 ], "4": [ 25440, 12640, 128 ], "5": [ 12720, 6320, 64 ], "6": [ 6360, 3160, 32 ], "7": [ 3180, 1580, 16 ], "8": [ 1590, 790, 8 ], "9": [ 795, 395, 4 ], "10": [ 398, 198, 2 ], "11": [ 199, 99, 1 ], "12": [ 100, 50, 0 ] },