BUG: Tests added for BinaryImageToLabelMapFilter for single-row images.

Change-Id: I910e787471871bb063c2f30a8454d2a89a6ecf3c
STYLE: Improve style in BinaryImageToLabelMapFilter.

Change-Id: Ie42b64449fdb9137a27e8d1b07d8bd0a09a5ea91
BUG: Fix BinaryImageToLabelMapFilter on 1D image.

The BinaryImageToLabelMapFilter partitions the input image into threads by
lines in the first dimension.  We cannot split along a scanline access.

Use an ImageRegionSplitterDirection with its Direction set to 0 to prevent
partitioning the threads on scannlines when there is only a single line.

Change-Id: I59c91e848cae9ee78653136241a8ced4f13ec5e7