Woops! Fix for previous F-Curve path fix commit

Trying to rename a valid F-Curve would crash as no RNA property was set, but
*prop still had an uninitialised value.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55073 954f8c5b-7b00-dc11-b283-0030488c597c