disallow filter changes when playing animations

• Load can.ex2.
• Add a Clip filter, defaults are fine.
• Run animation. Loop it so it repeats indefinitely.
• Now modify the clip filter with the widget in the Render View while the animation is running. Apply.
• Notice that the clip has not been modified and the animation is running from the cached timesteps.
• Now stop the animation. Change the plane again and click Apply. The geometry is updated.
• Run the animation again. The geometry is updated correctly the first time through.

To support this case, it may be best to disallow changes while animations are playing except camera changes, play, pause and such.