Crash when ventilation unit is shutdown

[Nuutti321]

A crash happens when the ventilation unit is shutdown for filter change or other purpose.

Logs:
2024-10-09T11:44:17.820Z [modbus] debug: Reading coil address 0, length 13
2024-10-09T11:44:22.827Z [modbus] error: Failed to read coil address 0, length 13
node:internal/process/promises:289
triggerUncaughtException(err, true /* fromPromise */);
^

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#".] {
code: 'ERR_UNHANDLED_REJECTION'
}

[Jalle19]

The error handling in general needs to be refactored so that there are no UnhandledPromiseRejection warnings thrown anymore, that will most likely fix this issue automatically.