Clean-up the nodata in the lower-left tile of the PaleoCAR dataset.

[jterstriep]

No description provided.

[tmcphillips]

Note that this is likely a distinct problem from that reported in issue #20. Here the issue is dealing with a nonexistent tile, and setting the pixel values in the corresponding region in the final data set with correct NODATA values. In issue #20 the issue is dealing with NODATA values in tiles present in the original data set files.