Fix for a crash due to the changes in the trunk revision 50087 for thread safety in curve evaluation.

Problem report from Vicente Carro with an example .blend file for reproducing the issue.  Thanks!

source/blender/freestyle/intern/python/BPy_Freestyle.cpp

@@ -208,6 +208,7 @@ static PyObject *Freestyle_evaluateCurveMappingF( PyObject *self, PyObject *args
 		return NULL;
 	}
 	cumap = (CurveMapping *)py_srna->ptr.data;
+	curvemapping_initialize(cumap);
 	/* disable extrapolation if enabled */
 	if ((cumap->cm[cur].flag & CUMA_EXTEND_EXTRAPOLATE)) {
 		cumap->cm[cur].flag &= ~( CUMA_EXTEND_EXTRAPOLATE );