Rounded Cube With 0 Radius Breaks #36

Expected result would be to simplify to just a Cube. Instead:

java.lang.Exception: java.lang.NumberFormatException: radius can not be negative
at com.neuronrobotics.bowlerstudio.scripting.ScriptingFileWidget$2.run(ScriptingFileWidget.java:337)
Caused by: java.lang.NumberFormatException: radius can not be negative
at eu.mihosoft.vrl.v3d.Sphere.toPolygons(Sphere.java:169)
at eu.mihosoft.vrl.v3d.Primitive.toCSG(Primitive.java:64)
at eu.mihosoft.vrl.v3d.RoundedCube.toPolygons(RoundedCube.java:103)
at eu.mihosoft.vrl.v3d.Primitive.toCSG(Primitive.java:64)
at eu.mihosoft.vrl.v3d.ItoCSG$toCSG.call(Unknown Source)