Fix "transmission without refraction" logic (#1742)

* Change possible 0^0 = 1 to 0^eps = 0

* different solution

* change pDiffuse to ray.color.w

chunky/src/java/se/llbit/chunky/renderer/scene/PathTracer.java

@@ -114,7 +114,7 @@ public static boolean pathTrace(Scene scene, Ray ray, WorkerState state,
         airDistance = ray.distance;
       }
 
-      if (pDiffuse + pSpecular < Ray.EPSILON && n1 == n2) {
+      if (ray.color.w + pSpecular < Ray.EPSILON && n1 == n2) {
         // Transmission without refraction.
         // This can happen when the ray passes through a transparent
         // material into another. It can also happen for example