Fix for bug reported by Thomas Dinges on IRC: OSL script node was not initializing the data_type variable for shader sockets and so tried to set a non-existing float RNA property, leading to failed assert.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56445 954f8c5b-7b00-dc11-b283-0030488c597c