fix(services): decode GetEventInformation without object identifier

[chowchin]

Problem

lastReceivedObjectIdentifier in a GetEventInformation request is optional (ASHRAE 135, 13.12.1.1). A client asking for the first batch of events omits it, so the request carries no service payload — but getEventInformation.decode reads the identifier unconditionally and runs past the end of the buffer.

The RangeError is raised inside the dgram message handler (_receiveData → _handleNpdu → _handlePdu → _processConfirmedServiceRequest), which application code cannot wrap, so one such request terminates the process of any device using bacstack to serve BACnet requests.

Reproduction — a request with no payload is a 10-byte datagram (BVLC 4 + NPDU 2 + APDU header 4), so client.js calls decode(buffer, 10, 0):

const service = require('./lib/services/get-event-information');
service.decode(Buffer.alloc(10), 10, 0);

master        : throws ERR_OUT_OF_RANGE - The value of "offset" is out of range. It must be >= 0 and <= 6. Received 11
with this fix : {"lastReceivedObjectId":null,"len":0}

Observed in production against a BMS that polls for alarms: every scan killed the gateway process, the service manager restarted it, the BMS retried and killed it again.

RangeError [ERR_OUT_OF_RANGE]: The value of "offset" is out of range. It must be >= 0 and <= 6. Received 11
    at Uint8Array.readUInt32BE (node:internal/buffer:309:5)
    at Object.decodeObjectId (lib/asn1.js:622:18)
    at Object.decode (lib/services/get-event-information.js:15:31)
    at Client._processConfirmedServiceRequest (lib/client.js:242:47)
    at Client._handlePdu (lib/client.js:413:16)
    at Client._handleNpdu (lib/client.js:437:10)

Change

Decode the identifier only when it is actually present, using the apduLen that client.js already passes, plus a check that the next tag really is context tag 0. When it is absent, lastReceivedObjectId is null and len is 0.

The third parameter is optional, so existing callers that pass only (buffer, offset) — including the current unit test — behave exactly as before.

Tests

Two cases added to test/unit/service-get-event-information.spec.js: a request without the optional identifier, and one whose buffer ends exactly at the offset. npm test passes (33 suites, 119 tests).