Fix Crawler::children() to not trigger a notice for childless node
merged branch lazyhammer/issue-8048 (PR #8054)

This PR was merged into the 2.1 branch.

Discussion
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[DomCrawler] Fix Crawler::children() to not trigger a notice for childless node

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8048
| License       | MIT
| Doc PR        | n/a

Commits
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91b8490 Fix Crawler::children() to not trigger a notice for childless node