Fix a bulge over a zero-length segment discarding the whole polyline

[redbluevn]

The problem

When any vertex carries a bulge, a polyline's bounding box is computed by tessellating each segment through Arc.CreateFromBulge.

A repeated vertex that still carries a bulge describes an arc over a chord of no length. Arc.GetCenter computes c = start.DistanceFrom(end) / 2.0 — zero — so radius = c / sin(theta/2) is exactly zero, and Circle's Radius setter throws:

if (value <= 0)
	throw new ArgumentOutOfRangeException(nameof(value), value, "The radius must be greater than 0.");

One such vertex therefore threw away the measurement of the entire polyline — and, because polylines live inside blocks, of every insert of that block.

Duplicated vertices are common in real exports.

The fix

Such a segment covers no ground, so it contributes its endpoints and nothing else.

Evidence

Across eighteen architectural drawings: two zero-length bulged segments, one of them throwing. After this, no entity in the corpus fails to report a box. The only remaining non-measurable entities are Regions, which return BoundingBox.Null by design because modeler geometry is not tessellated — that is not a defect and is left alone.

Adjacent, not fixed here

Three more paths can throw out of GetBoundingBox for the same reason — a raw value the readers store faithfully and an entity setter refuses:

• Hatch.BoundaryPath.Arc.GetBoundingBox builds an Arc entity, so an edge with radius ≤ 0 throws. (The entity reader already clamps this — DwgObjectReader maps radius <= 0 to MathHelper.Epsilon — but the boundary-edge reader does not.)
• Hatch.BoundaryPath.Ellipse.GetBoundingBox builds an Ellipse, so an edge ratio of 0 or above 1 throws.
• BlockRecord.GetBoundingBox evaluates every child's box twice, once for the infinite check and once for the merge — quadratic through nested blocks.

None of the three occurs in my corpus (measured: 0, 0, and the double evaluation is a cost not a fault), so I have left them out rather than ship unexercised code. Raising them in case they are worth a separate look.

Tests

ABulgeOverAZeroLengthSegmentDoesNotThrow fails against the current code with ArgumentOutOfRangeException.

dotnet test: 2314 passed / 17 failed, against master at 592d70a on this machine at 2313 / 17.

Related

#1223, #1224, #1225, #1226, #1227 and DomCR/CSUtilities#23.