Add missing JNI configuration

Author: atextor

core/esmf-native-support/src/main/java/org/eclipse/esmf/nativefeatures/DiagramFeature.java

@@ -278,7 +278,7 @@ private void setupAwt() {
                   "supportsAlpha", "transparency" )
             .registerMethodForJni( "getRGBdefault" );
       Native.forClass( java.awt.image.IndexColorModel.class )
-            .registerFieldsForJni( "allgrayopaque", "map_size", "rgb", "transparent_index" );
+            .registerFieldsForJni( "allgrayopaque", "map_size", "rgb", "transparent_index", "colorData" );
       Native.forClass( "sun.awt.AWTAutoShutdown" )
             .registerMethodForJni( "notifyToolkitThreadBusy" )
             .registerMethodForJni( "notifyToolkitThreadFree" );