Subject: [PATCH] BRepMesh: take the seam pcurve point at the edge parameter

Taken from OrcaSlicer 2.5.0 deps/OCCT, which applies it to its bundled
OCCT 8.0.1. A Geom2d_Line's FirstParameter() is -Precision::Infinite(),
so the seam check failed and cone faces with a slightly tilted seam
pcurve were not triangulated. Upstream issue Open-Cascade-SAS/OCCT#572.

diff --git a/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx b/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
index 6f63781..9b1c08e 100644
--- a/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
+++ b/src/ModelingAlgorithms/TKMesh/BRepMesh/BRepMesh_ModelPreProcessor.cxx
@@ -210,10 +210,10 @@ private:
 
     // Define two pcurves of the seam-edge.
     occ::handle<Geom2d_Curve> aPC1, aPC2;
-    double                    af, al;
+    double                    af, al, af1, al1;
 
     aE.Orientation(TopAbs_FORWARD);
-    aPC1 = BRep_Tool::CurveOnSurface(aE, aF, af, al);
+    aPC1 = BRep_Tool::CurveOnSurface(aE, aF, af1, al1);
 
     aE.Orientation(TopAbs_REVERSED);
     aPC2 = BRep_Tool::CurveOnSurface(aE, aF, af, al);
@@ -224,7 +224,9 @@ private:
     }
 
     // Select the correct pcurve of the seam-edge.
-    const gp_Pnt2d& aFPntOfPC1 = aPC1->Value(aPC1->FirstParameter());
+    // Use the edge's first parameter. A Geom2d_Line's FirstParameter() is -Precision::Infinite(),
+    // where a direction of (2e-16, -1) from rounding error gives an X far outside the U range.
+    const gp_Pnt2d aFPntOfPC1 = aPC1->Value(af1);
 
     if (std::abs(aLPntOfIPC1.X() - aFPntOfPC1.X()) > Precision::Confusion())
     {