return 0 if there is no valid data
merged branch dominikzogg/timecollectorfix (PR #8581)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #8581).

Discussion
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TimeCollector, Notice, if no events

https://github.com/symfony/symfony/issues/8574

Commits
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e9da1c0 return 0 if there is no valid data