Photons remain frozen when sim is launched

[KatieWoe]

Found during https://github.com/phetsims/phet-io/issues/1626.
If there are photons on the screen when the sim is launched, the photons freeze in place in the launched sim and do not move. Switching the light source seems to get rid of them.

[zepumph]

Excellent. This seems to be a state bug. We will get to this next time we work on the sim. Tagging @jessegreenberg and @jbphet so they are away in case they need to publish greenhouse + MAL with phet-io state support sooner rather than later (I don't think that's true).