1388 crash when usind draw fused aircraft triangulation

[joergbrech]

Note: This PR was AI-generated (Claude Code) and reviewed/verified by me before submission.

Description

Fixes #1388.

Fusing the whole aircraft (Draw -> Aircraft -> Fused aircraft triangulation (slow) in TiGLCreator) crashed with:

terminate called after throwing an instance of 'tigl::CTiglError'
  what():  No geometry primitives defined for uID="ceiling_PanelingElements_0000"

This had two causes, both fixed here:

1. Fuse aborted on components without geometry. CTiglElementGeometryBuilder::BuildShape() threw whenever a system or deck component (e.g. a lavatory or ceiling panel) had no <geometry> primitives defined. This is a perfectly valid CPACS state — all primitive lists inside <geometry> are optional, so an element can legitimately be described by mass properties only. BuildShape()now returns a null shape in that case instead of throwing, consistent with how the rest of the codebase already treats "no shape" (e.g. ducts, mirrored lofts, far field,CFuseShapes/CGroupShapes` already skip null shapes when aggregating).

   The two call sites that genuinely need a shape to do their job —
   CCPACSComponent::GetCentroidLocal() and the BuildMass() implementations in
   CCPACSComponent and CCPACSDeckComponentBase (for volume-based mass/CoG) — now explicitly
   check for the missing geometry and report a precise error there instead, rather than the fuse
   algorithm blowing up mid-way through an unrelated multi-minute operation.

2.Uncaught exception in TiGLCreator. TIGLCreatorDocument::drawFusedAircraftTriangulation() never caught exceptions from the fusing algorithm, so any remaining CTiglError (or any other exception) would terminate the whole application. It now wraps the fuse call in the same try/catch used by drawFusedAircraft(), showing an error dialog instead of crashing.

How Has This Been Tested?

• Added InvalidSystems.ElementWithoutGeometryHasNoLoft (tests/unittests/tiglSystems.cpp): confirms GetLoft() on a system component without geometry returns a null shape instead of throwing.
• Updated InvalidSystems.InvalidSystemMassProperties: the "no geometry" case now surfaces as a precise "zero volume" error from the mass computation (which genuinely needs a shape) instead of an opaque "no geometry primitives" error from loft building.
• Added Decks.ComponentWithoutGeometryHasNoLoft and, most importantly, Decks.FusingToleratesComponentWithoutGeometry (tests/unittests/tiglDecks.cpp), an end-to-end regression test that fuses a small aircraft (TestData/simpletest-decks.cpacs.xml, extended with a new mass-only lavatory element/instance) via CCPACSConfiguration::AircraftFusingAlgo()->FusedPlane() and asserts it no longer throws.
• Verified both new tests actually catch the regression: temporarily reverted the CTiglElementGeometryBuilder::BuildShape() fix and confirmed both tests fail with the original No geometry primitives defined for uID="..." exception, then restored the fix and confirmed they pass again.
• Ran the full unit test suite (pixi run -e default unittests): 901/901 tests pass, no regressions.

Screenshots, that help to understand the changes(if applicablable):

N/A (backend/logic fix, no UI changes)

Checklist for PR Author:

• Unit or integration test added (if applicable)
• Python interface updated (if applicable) — not needed, no public API change
• Python test added (if Python interface updated) — not need
• Doxygen docstrings added — not needed (no new public API), added a code comment explaining the new null-return behavior
• ChangeLog.md updated

[github-actions]

PR Reminders

This PR has changes in src/, TIGLCreator/, and tests/unittests/ but not in tests/integrationtests/, tests/python/, or bindings/python_internal/. ChangeLog.md has changes.

• 💡 Tip: Please check if new classes need to be added to the Python bindings

---

This is an automated reminder from CI

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.23%. Comparing base (76802f0) to head (1b8e941).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1389      +/-   ##
==========================================
+ Coverage   73.21%   73.23%   +0.01%     
==========================================
  Files         324      324              
  Lines       28556    28563       +7     
==========================================
+ Hits        20908    20918      +10     
+ Misses       7648     7645       -3     

Flag	Coverage Δ
unittests	73.23% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/decks/CCPACSDeckComponentBase.cpp	96.74% <100.00%> (+0.05%)	⬆️
src/geometry/CTiglElementGeometryBuilder.cpp	100.00% <100.00%> (ø)
src/systems/CCPACSComponent.cpp	92.98% <100.00%> (+0.52%)	⬆️

... and 2 files with indirect coverage changes

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