Fix typo in error message

git-svn-id: http://svn.osgeo.org/postgis/trunk@12454 b70326c6-7e19-0410-871a-916f4a2858ee
Do not allow loading offline rasters when explicitly disabled

Previous commit only disabled _saving_ rasters with offline flag,
this one prevents actually loading the offline data.
You can still dump databases with offline raster specs.

git-svn-id: http://svn.osgeo.org/postgis/trunk@12455 b70326c6-7e19-0410-871a-916f4a2858ee