default-TV switch state file getting corrupted
I've noticed that if homebridge crashes the file can get corrupted and homebridge fails to start, till I fix this manually. 

Any way you can add a check if the file is valid and if it's not create a new one?


```
[2018-4-18 07:22:30] [Broadlink RM] Initializing BroadlinkRM platform...

C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\node-persist\src\local-storage.js:666
            throw Error('[PARSE-ERROR] ' + file + ' does not look like a valid storage file!');
                  ^
Error: [PARSE-ERROR] C:\Users\pax07\.homebridge\plugin-persist\homebridge-broadlink-rm\407914695a1dc129bbf2ef7dc9e2450a does not look like a valid storage file!
    at LocalStorage.parseFileSync (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\node-persist\src\local-storage.js:666:19)
    at LocalStorage.parseStorageDirSync (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\node-persist\src\local-storage.js:615:26)
    at LocalStorage.initSync (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\node-persist\src\local-storage.js:142:14)
    at Object.nodePersist.initSync (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\node-persist\src\node-persist.js:37:32)
    at Object.init (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\homebridge-platform-helper\helpers\persistentState.js:9:15)
    at new HomebridgePlatform (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\node_modules\homebridge-platform-helper\platform.js:15:21)
    at new BroadlinkRMPlatform (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge-broadlink-rm\platform.js:31:5)
    at Server._loadPlatforms (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge\lib\server.js:304:32)
    at Server.run (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge\lib\server.js:85:36)
    at module.exports (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge\lib\cli.js:40:10)
    at Object.<anonymous> (C:\Users\pax07\AppData\Roaming\npm\node_modules\homebridge\bin\homebridge:17:22)
    at Module._compile (module.js:662:30)
    at Object.Module._extensions..js (module.js:673:10)
    at Module.load (module.js:575:32)
    at tryModuleLoad (module.js:515:12)
    at Function.Module._load (module.js:507:3)
    at Function.Module.runMain (module.js:703:10)
    at startup (bootstrap_node.js:193:16)
    at bootstrap_node.js:660:3
```