Fix out-of-bounds panic in RTA fetchServices when no PMM agent is found

[Copilot]

Accessing pmmAgents[0] without a bounds check in fetchServices causes a panic when FindPMMAgentsForService returns an empty slice — a valid scenario for a service with no associated PMM agent.

Changes

• managed/services/realtimeanalytics/service.go: Added len(pmmAgents) == 0 guard in fetchServices before accessing the first element; services with no PMM agent are silently skipped, consistent with the existing behavior for unsupported agent versions.

if len(pmmAgents) == 0 {
    // skip services without pmm-agent
    return nil
}

if !isPmmAgentSupportRta(pointer.Get(pointer.Get(pmmAgents[0]).Version)) {
    // skip services with unsupported pmm-agent version
    return nil
}

PMM-14900

Link to the Feature Build: SUBMODULES-0

If this PR adds, removes or alters one or more API endpoints, please review and add or update the relevant API documentation as well:

• API Docs updated

If this PR is related to some other PRs in this or other repositories, please provide links to those PRs:

• Original PR: PMM-14900 Add protection to RTA session against unsupported pmm-agent version #5116

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[it-percona-cla]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}