Crash if an empty array is passed in

[HannahMitt]

I can handle the empty check myself, but it might be a good case to check for.

The error happens on this line in GraphView

            highest = values[values.length-1].valueX;

Stack trace:

java.lang.ArrayIndexOutOfBoundsException: length=0; index=-1
E/AndroidRuntime(31521): at com.jjoe64.graphview.GraphView.getMaxX(GraphView.java:469)
E/AndroidRuntime(31521): at com.jjoe64.graphview.GraphView$GraphViewContentView.onDraw(GraphView.java:67)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13458)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13342)
E/AndroidRuntime(31521): at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
E/AndroidRuntime(31521): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13340)
E/AndroidRuntime(31521): at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
E/AndroidRuntime(31521): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13340)
E/AndroidRuntime(31521): at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
E/AndroidRuntime(31521): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13340)
E/AndroidRuntime(31521): at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
E/AndroidRuntime(31521): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13340)
E/AndroidRuntime(31521): at android.view.ViewGroup.drawChild(ViewGroup.java:2929)
E/AndroidRuntime(31521): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2799)
E/AndroidRuntime(31521): at android.view.View.draw(View.java:13461)
E/AndroidRuntime(31521): at android.widget.FrameLayout.draw(FrameLayout.java:467)
E/AndroidRuntime(31521): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2183)
E/AndroidRuntime(31521): at android.view.ViewRootImpl.drawSoftware(ViewRootImpl.java:2256)
E/AndroidRuntime(31521): at android.view.ViewRootImpl.draw(ViewRootImpl.java:2151)
E/AndroidRuntime(31521): at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2019)
E/AndroidRuntime(31521): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1830)
E/AndroidRuntime(31521): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
E/AndroidRuntime(31521): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
E/AndroidRuntime(31521): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
E/AndroidRuntime(31521): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
E/AndroidRuntime(31521): at android.view.Choreographer.doFrame(Choreographer.java:525)
E/AndroidRuntime(31521): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
E/AndroidRuntime(31521): at android.os.Handler.handleCallback(Handler.java:615)
E/AndroidRuntime(31521): at android.os.Handler.dispatchMessage(Handler.java:92)
E/AndroidRuntime(31521): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(31521): at android.app.ActivityThread.main(ActivityThread.java:4745)
E/AndroidRuntime(31521): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(31521): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(31521): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
E/AndroidRuntime(31521): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime(31521): at dalvik.system.NativeStart.main(Native Method)