Fix for missing letters when V-carving a string.

Issue 8064 occurs when FreeCAD passes a Voronoi diagram to
Boost that becomes self-intersecting when Boost truncates the
diagram's coordinates to integers.  This occurs when the discretizer
slightly misses closing the polygon generated for the letter by less
that FreeCAD's epsilon, then the wrapping Python code closes the
polygon by adding the initial polygon point as the final point.
This creates a short segment that, depending on the position of
the letter in the coordinate system, may end up being moved one
Boost coordinate delta away from the intended point, which can
end up self-intersecting.
Since the miss is very small, FreeCAD should treat it as it it
were the initial point.  There's no need for a duplicate copy of
the initial point, so we remove this point close to the initial
point and let insert_many_wires() close the polygon as usual.

src/Mod/Path/Path/Op/Vcarve.py

@@ -264,9 +264,24 @@ class ObjectVcarve(PathEngraveBase.ObjectOp):
                 Path.Log.debug("discretize value: {}".format(obj.Discretize))
                 pts = wire.discretize(QuasiDeflection=obj.Discretize)
                 ptv = [FreeCAD.Vector(p.x, p.y) for p in pts]
+                # Check over the last point before just closing the polygon
+                # by adding the start again.  If the discretizer was aiming
+                # for the last point and missed by a little bit, closing the
+                # polygon as is could result in OpenVoronoi truncating the
+                # coordinates to a self-intersecting polygon which is invalid.
+                # Instead, if the last point is close to the first, remove it
+                # and let the final append close the polygon.
+                # See issue 8064
+                if len(ptv) > 0:
+                    dist = ptv[-1].distanceToPoint(ptv[0])
+                    if dist < FreeCAD.Base.Precision.confusion():
+                        Path.Log.debug(
+                            "Removing bad carve point: {} from polygon origin"
+                            .format(dist))
+                        del ptv[-1]
                 ptv.append(ptv[0])
 
-                for i in range(len(pts)):
+                for i in range(len(ptv)-1):
                     vd.addSegment(ptv[i], ptv[i + 1])
 
         def cutWire(edges):