Fix resource leak issue - 372

Scenario - If we have multiple level of parents for chart widget and If
we dispose bottom most(top most is chart) widget by invoking dispose
chart widget get disposed without calling chart.dispose(). Any
subsequent call to dispose never calls dispose for it's children. So
checking if chart disposed in the dispose method never give an
opportunity to children dispose in the above Scenario. I have added
chart disposed safety check at Title because this was causing the issue
#289.

Fixes #372

org.eclipse.swtchart/src/org/eclipse/swtchart/Chart.java

@@ -386,12 +386,10 @@ public void update() {
 	@Override
 	public void dispose() {
 
-		if(!isDisposed()) {
-			title.dispose();
-			legend.dispose();
-			axisSet.dispose();
-			super.dispose();
-		}
+		title.dispose();
+		legend.dispose();
+		axisSet.dispose();
+		super.dispose();
 	}
 
 	@Override

org.eclipse.swtchart/src/org/eclipse/swtchart/internal/Title.java

@@ -277,8 +277,9 @@ public ChartLayoutData getLayoutData() {
 	 * Disposes the resources.
 	 */
 	public void dispose() {
-
-		chart.removePaintListener(this);
+		if(!chart.isDisposed()) {
+			chart.removePaintListener(this);
+		}
 	}
 
 	@Override