TIFF: adjust optimal tile height if tiles have height of 1 (rebased onto develop)



This is the same as gh-1009 but rebased onto develop.

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This prevents callers that rely on the optimal tile height from reading
one row at a time from small images.  If the images are sufficiently
wide that only 1 row of pixels will fit in memory, then the optimal
height will still be 1.

Fixes http://trac.openmicroscopy.org.uk/ome/ticket/11850