GTiff: when compiling against internal libtiff, in read-only mode, optimization to avoid fetching the whole Strip/TileCounts and Strip/TileOffsets arrays

git-svn-id: https://svn.osgeo.org/gdal/trunk@26685 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx