Don't add SiblingOrder when specialising the first element of an archetype

[VeraPrinsen]

Example of the bug:

flat parent archetype:

CLUSTER
   ELEMENT[id2]
   ELEMENT[id4]

flat child archetype:

CLUSTER
   ELEMENT[id2]
   ELEMENT[id2.1]
   ELEMENT[id4]

Expected differentiated archetype:

CLUSTER
   ELEMENT[id2.1]

What comes out of the differentiator at the moment:

CLUSTER
   after[id2]
   ELEMENT[id2.1]

This gives errors when flattening the archetype, and puts the specialised id2.1 element last instead of at the place of the original id2 element.

Problem was in the 'handleDirectlyAfterSameParentNode' method where the parent id code was found, but because the for loop ended, the method still returned 'false', even though there was a parent node that this specialised element could go right after.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.80%. Comparing base (e36d98e) to head (d98ac4f).

Files	Patch %	Lines
...in/java/com/nedap/archie/diff/LCSOrderingDiff.java	75.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #604 +/- ## ============================================ - Coverage 71.80% 71.80% -0.01% + Complexity 6956 6955 -1 ============================================ Files 663 663 Lines 22691 22690 -1 Branches 3676 3676 ============================================ - Hits 16294 16292 -2 Misses 4664 4664 - Partials 1733 1734 +1 ```

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