[HttpKernel] Improve TraceableEventDispatcher to not call Stopwatch::stop() when not started
merged branch Olden/issue_7639 (PR #7653)

This PR was squashed before being merged into the master branch (closes #7653).

Discussion
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[HttpKernel] Improve TraceableEventDispatcher to not call Stopwatch::stop() when not started

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7639
| License       | MIT

Commits
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e638e01 [HttpKernel] Improve TraceableEventDispatcher to not call Stopwatch::stop() when not started