fix #10581: getTile byte-ordering issue

See:
 * http://trac.openmicroscopy.org.uk/ome/ticket/10581#comment:7
 * https://github.com/openmicroscopy/openmicroscopy/pull/1359

`getTile()` method was missing a call to `reader.swapIfRequired()`. Test added by @will-moore in gh-1359 now passes along with the rest of `gatewaytest/pixels.py`. Hopefully the rest of the suite will stay green tomorrow.

/cc @chris-allan, @will-moore, @melissalinkert