Fixed bug where Flash photo taker would fail

So it seems like the event handler that was supposed to toggle permissionGiven fails to trigger when you've set Flash permissions to "always allow camera from X site" (as opposed to "allow this time"), which is the only good way to enable the camera in Safari.

Switched the code to just use "cam.muted" to check whether or not the camera is accessible, since this setting is always accurate.

@ormsbee (also, if you have any idea who'd be a good second reviewer for this, let me know)

LMS-1487