Gh-3215: Fix HasStep filtering

[p29876]

Related issue

• Resolve #3215

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.95775% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 66.96%. Comparing base (8df736a) to head (b808dc4).

Files	Patch %	Lines
...pop/process/traversal/step/GafferPopGraphStep.java	89.36%	1 Missing and 4 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3216 +/- ## ============================================= + Coverage 66.89% 66.96% +0.07% + Complexity 2558 2556 -2 ============================================= Files 912 912 Lines 29303 29366 +63 Branches 3267 3273 +6 ============================================= + Hits 19602 19665 +63 + Misses 8256 8254 -2 - Partials 1445 1447 +2 ```

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