close dead connections even if they have active subscriptions

[tharu-jwd]

Description

The heartbeat was skipping termination for dead clients that had active subscriptions. Removed !this.subscriptions.size guard from onHeartbeat() as the solution.

Related Issue

Fixes #427

Motivation and Context

Dead clients with subscriptions were kept alive forever. Server kept pinging them, matching events against their filters, leaking memory.

How Has This Been Tested?

Manually connected a client, sent a REQ, killed it abruptly, confirmed the server closes it on the next heartbeat cycle instead of continuing to ping.

Screenshots (if appropriate):

N/A

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• All new and existing tests passed.