Moved the WMS layer name encoding to be done before the sub datasets URLs are created.

From: Tim Astle <tastle@caris.com>

git-svn-id: https://svn.osgeo.org/gdal/trunk@27892 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx