fix urquhartFaces() for unconstrained tins

Author: micycle1

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `PGS_Morphology.rounding()` no longer gives invalid results.
 * `PGS_ShapePredicates.elongation()` now correctly measures shape elongation (previously inverted, now returns 1 for highly elongated shapes).
 * `PGS_Conversion.toGraph()` now processes `LINES` shapes correctly.
+* `PGS_Meshing.urquhartFaces()` no longer errors on triangulation inputs with no constraints.
 
 ### Removed
 

src/main/java/micycle/pgs/PGS_Meshing.java

@@ -511,6 +511,9 @@ public static PShape centroidQuadrangulation(final IIncrementalTin triangulation
 	 */
 	private static PShape removeHoles(PShape faces, IIncrementalTin triangulation) {
 		List<IConstraint> holes = new ArrayList<>(triangulation.getConstraints()); // copy list
+		if (holes.size() <= 1) {
+			return faces;
+		}
 		holes = holes.subList(1, holes.size()); // slice off perimeter constraint (not a hole)
 
 		STRtree tree = new STRtree();