Initialize blend radius with 0

Otherwise that might trigger the negative check for motion primitives
that don't explicitly set it.

Author: urfeex

include/ur_client_library/control/motion_primitives.h

@@ -68,7 +68,7 @@ struct MotionPrimitive
   std::chrono::duration<double> duration;
   double acceleration;
   double velocity;
-  double blend_radius;
+  double blend_radius = 0.0;
 
   virtual bool validate() const;
 };