Basically you have a couple of options for the shooter.
1. Cock right pistol and proceed with the stage.
2. Stop: Ask TO for a restart. Upon ok from TO shooter would holster left pistol. Then under supervision of TO would make pistol safe with hammer fully down on empty chamber. Then holster right pistol and get ready to re-start the stage after saying your line !
It is up to the shooter to proceed or stop.
JM