Fix ShapeSDF in case no distortion map is given

orx-jumpflood/src/demo/kotlin/DemoShapeSDF03.kt

@@ -39,7 +39,6 @@ fun main() {
                 }
             }
             extend {
-
                 drawer.background(ColorRGBa.PINK)
 
                 fd.apply(emptyArray(), uvmap)

orx-jumpflood/src/main/kotlin/ShapeSDF.kt

@@ -73,6 +73,8 @@ class ShapeSDF : Filter(filterShaderFromUrl(resourceUrl("/shaders/gl3/shape-sdf.
         parameters["fromBuffer"] = fromBuffer
         parameters["toBuffer"] = toBuffer
         parameters["segmentCount"] = segmentCount
-        super.apply(source, target)
+        // -- bit of an hack
+        val effectiveSource = if (source.isNotEmpty()) source else target
+        super.apply(effectiveSource, target)
     }
 }