docs: correct pager has_next examples

[ricellis]

PR summary

Various fixes for pagination

Fixes: s1189

Note: An existing issue is required before opening a PR.

PR Checklist

Please make sure that your PR fulfills the following requirements:

• The commit message follows the
  Angular Commit Message Guidelines.
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

What is the current behavior?

The new pagination feature code (unreleased) from #819 had a few bugs.

• Example code used get_next instead of has_next in if check

What is the new behavior?

• Correct examples to use has_next

Does this PR introduce a breaking change?

• Yes
• No

Other information