fixed wavefront when negative vertex index

Author: andresoviedo

app/build/outputs/apk/release/app-release.apk

@@ -2,8 +2,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           xmlns:tools="http://schemas.android.com/tools"
     package="org.andresoviedo.dddmodel2"
-    android:versionCode="20"
-    android:versionName="2.5.0" >
+    android:versionCode="21"
+    android:versionName="2.5.1" >
 
     <uses-sdk
         android:minSdkVersion=""