Chamfered Cube Refuses to Make 0 Width Edge

[JansenSmith]

Both of these commits should work:
JansenSmith/ChamferedParts_JansenSmith@385da70
JansenSmith/ChamferedParts_JansenSmith@d3cea8a

Second commit instead does:

script error
java.lang.Exception: java.lang.NumberFormatException: Z can not be negative
	at com.neuronrobotics.bowlerstudio.scripting.ScriptingFileWidget$2.run(ScriptingFileWidget.java:337)
Caused by: java.lang.NumberFormatException: Z can not be negative
	at eu.mihosoft.vrl.v3d.Cube.toPolygons(Cube.java:127)
	at eu.mihosoft.vrl.v3d.Primitive.toCSG(Primitive.java:64)
	at eu.mihosoft.vrl.v3d.ChamferedCube.toPolygons(ChamferedCube.java:38)
	at eu.mihosoft.vrl.v3d.Primitive.toCSG(Primitive.java:64)
	at eu.mihosoft.vrl.v3d.ItoCSG$toCSG.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)