- Avoid potential cast error

refs 1841

org.fortiss.tooling.base.ui/trunk/src/org/fortiss/tooling/base/ui/annotation/view/AnnotationViewPartBase.java

@@ -100,7 +100,7 @@ public abstract class AnnotationViewPartBase extends ViewPart implements ISelect
 		if(currentlySelectedObject == null) {
 			ElementEditPartBase<?> editPart =
 					SelectionUtils.checkAndPickFirst(selection, ElementEditPartBase.class);
-			if(editPart != null) {
+			if(editPart != null && editPart.getModel() instanceof IModelElement) {
 				currentlySelectedObject = (IModelElement)editPart.getModel();
 			} else {
 				// Not all editors are derived from ElementEditPartBase, most notably