WillAppear State should be optional

[PaigeM89]

The WillAppear event will only send the state field if the manifest.json defines multiple states. When only a single state is defined, the deserialization fails.

For readability, here's the relevant info broken out:

TRCE Received message {
  "action":"org.paigem89.sendmessage",
  "context":"A7CD0413F617CCD76B8DBEC26DE2DC93",
  "device":"89BFC41A68A05A303471FEA4EE372FA8",
  "event":"willAppear",
  "payload":{"coordinates":{"column":0,"row":2},"isInMultiAction":false,"settings":{}}
}

ERRO read error: BadMessage(Error("missing field `state`", line: 0, column: 0))

Relevant section of the Elgato docs here.

Here's the full stack trace:

Aug 22 18:23:19.068 TRCE received frame 
<FRAME>
final: true
reserved: false false false
opcode: TEXT
length: 236
payload length: 232
payload: 0x7b22616374696f6e223a226f72672e70616967656d38392e73656e646d657373616765222c22636f6e74657874223a224137434430343133463631374343443736423844424543323644453244433933222c22646576696365223a223839424643343141363841303541333033343731464541344545333732464138222c226576656e74223a2277696c6c417070656172222c227061796c6f6164223a7b22636f6f7264696e61746573223a7b22636f6c756d6e223a302c22726f77223a327d2c226973496e4d756c7469416374696f6e223a66616c73652c2273657474696e6773223a7b7d7d7d
            
Aug 22 18:23:19.068 TRCE Received message {"action":"org.paigem89.sendmessage","context":"A7CD0413F617CCD76B8DBEC26DE2DC93","device":"89BFC41A68A05A303471FEA4EE372FA8","event":"willAppear","payload":{"coordinates":{"column":0,"row":2},"isInMultiAction":false,"settings":{}}}
Aug 22 18:23:19.069 ERRO read error: BadMessage(Error("missing field `state`", line: 0, column: 0))