ISIS3: fix to recognize IsisCube.Mapping.LatitudeType = Planetocentric (#5717, by Trent Hare)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27909 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx