Added defaults for slider state (#9734)

shared/src/com/vaadin/shared/ui/slider/SliderState.java

@@ -6,15 +6,15 @@ public class SliderState extends AbstractFieldState {
 
     public double value;
 
-    public double maxValue;
-    public double minValue;
+    public double maxValue = 100;
+    public double minValue = 0;
 
     /**
      * The number of fractional digits that are considered significant. Must be
      * non-negative.
      */
-    public int resolution;
+    public int resolution = 0;
 
-    public SliderOrientation orientation;
+    public SliderOrientation orientation = SliderOrientation.HORIZONTAL;
 
 }