fix #9917: adjust tile drawing for big images (rebased onto develop)



This is the same as gh-1444 but rebased onto develop.

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Try to reproduce https://trac.openmicroscopy.org.uk/ome/ticket/9917 using OpenGL Insight. `test_images_good/cellsens/brian/_BZ cfos1-2_05_/` is a great test. Make sure that all the tiles appear in the full image viewer, at the correct aspect ratio.