Fixed NULL transfer function issue.
Fixed NULL transfer function issue.

Transfer get1DTransferFunction from Lua1DTransferFunctionProxy would
always return NULL when used after a call to Set1DTrans.

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@2497 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok