[webpubsubclient] Fix a bug that 0 sequenceId won't be sent to service

[zackliu]

Packages impacted by this PR

@azure/web-pubsub-client

Issues associated with this PR

Describe the problem that is addressed by this PR

In the previous RP, we found a bug that if sequenceId == 0, then it won't be sent to the service. Which means if no message is received from the service, there won't be a keepalive enabled

What are the possible designs available to address the problem? If there are more than one possible design, why was the one in this PR chosen?

Are there test cases added in this PR? (If not, why?)

Yes

Provide a list of related PRs (if any)

Command used to generate this PR:**(Applicable only to SDK release request PRs)

Checklists

• [x] Added impacted package name to the issue description
• [ ] Does this PR needs any fixes in the SDK Generator?** (If so, create an Issue in the Autorest/typescript repository and link it here)
• [x] Added a changelog (if necessary)

[azure-sdk]

API change check

API changes are not detected in this pull request.

[zackliu]

@xirzec Could you help to merge

[xirzec]

@xirzec Could you help to merge

Done!