Merge pull request #773 from jbousquie/fix.tube

fix tube arc parameter

src/Mesh/babylon.meshBuilder.ts

@@ -390,6 +390,7 @@
             var updatable = options.updatable;
             var sideOrientation = options.sideOrientation || Mesh.DEFAULTSIDE;
             var instance = options.instance;
+            options.arc = (options.arc < 0) ? 1 : options.arc || 1;
 
             // tube geometry
             var tubePathArray = (path, path3D, circlePaths, radius, tessellation, radiusFunction, cap, arc) => {