fix: align BuildPath tiny-triangle check with upstream

Co-authored-by: micycle1 <9304234+micycle1@users.noreply.github.com>

Author: Copilot

src/main/java/clipper2/engine/ClipperBase.java

@@ -2793,7 +2793,7 @@ public static boolean BuildPath(@Nullable OutPt op, boolean reverse, boolean isO
 			}
 		}
 
-		if (path.size() == 3 && IsVerySmallTriangle(op2)) {
+		if (path.size() == 3 && !isOpen && IsVerySmallTriangle(op2)) {
 			return false;
 		} else {
 			return true;