guard against race condition
guard against race condition

`run` uses `setTimeout` to invoke `client.sync()` in the future.

but if the user disables the ledger before then, hilarity ensues.

this patch prevents that from happening…

MKuenzi/browser-laptop,dcposch/browser-laptop,darkdh/browser-laptop,jonathansampson/browser-laptop,jonathansampson/browser-laptop,Sh1d0w/browser-laptop,darkdh/browser-laptop,jonathansampson/browser-laptop,willy-b/browser-laptop,MKuenzi/browser-laptop,MKuenzi/browser-laptop,willy-b/browser-laptop,diasdavid/browser-laptop,dcposch/browser-laptop,pmkary/braver,luixxiul/browser-laptop,willy-b/browser-laptop,timborden/browser-laptop,darkdh/browser-laptop,diasdavid/browser-laptop,pmkary/braver,dcposch/browser-laptop,timborden/browser-laptop,Sh1d0w/browser-laptop,darkdh/browser-laptop,diasdavid/browser-laptop,jonathansampson/browser-laptop,timborden/browser-laptop,willy-b/browser-laptop,luixxiul/browser-laptop,Sh1d0w/browser-laptop,pmkary/braver,luixxiul/browser-laptop,dcposch/browser-laptop,MKuenzi/browser-laptop,timborden/browser-laptop,pmkary/braver,Sh1d0w/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop