EvaluateExpression now throws an exception when no raster data block is found in the first volume.
EvaluateExpression now throws an exception when no raster data block is found in the first volume.

git-svn-id: 353be9ac11a1e711854a13efcc2fc17d9d6b83e7@1773 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok