SDK : fixed NPE in colorRGBADIalog introduced by previous change

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@7973 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

sdk/jme3-materialeditor/src/com/jme3/gde/materials/multiview/widgets/ColorRGBADialog.java

@@ -165,10 +165,12 @@ public class ColorRGBADialog extends javax.swing.JDialog {
     }
 
     public void setColor(Color color) {
-        this.color = color;
-        jColorChooser1.setColor(color);
-        
-        alphaSlider.setValue((int) ((float) (color.getAlpha() / 255f) * 100));
+        if (color != null) {
+            this.color = color;
+            jColorChooser1.setColor(color);
+
+            alphaSlider.setValue((int) ((float) (color.getAlpha() / 255f) * 100));
+        }
 
     }
 }