fix curve template mapping evaluate

Created by: zeffii

fixes curve evaluate

using

def get_valid_evaluate_function2(mat_name, node_name):
    ''' 
    Takes a material name (cycles) and a Node name it expects to find.
    The node will be of type ShaderNodeRGBCurve and this function
    will force its existence, then return the evaluate function for the last
    component of RGBA - allowing us to use this as a float modifier.
    '''

    node = get_valid_node(mat_name, node_name, 'ShaderNodeRGBCurve')

    curve = node.mapping.curves[3]
    try:  node.mapping.evaluate(curve, 0.0)
    except: node.mapping.initialize()

    evaluate = lambda val: node.mapping.evaluate(curve, val)
    return evaluate