Fix occasional widget disposed exception

git-svn-id: http://dev.eclipse.org/svnroot/technology/org.eclipse.stem/branches/STEM_1_4_0@3453 92a21009-5b66-0410-b83a-dc787c41c6e9

core/org.eclipse.stem.ui/src/org/eclipse/stem/ui/widgets/DecoratorSelector.java

diff --git a/core/org.eclipse.stem.ui/src/org/eclipse/stem/ui/widgets/DecoratorSelector.java b/core/org.eclipse.stem.ui/src/org/eclipse/stem/ui/widgets/DecoratorSelector.java
index 1e35db2..bb0a257 100644
--- a/core/org.eclipse.stem.ui/src/org/eclipse/stem/ui/widgets/DecoratorSelector.java
+++ b/core/org.eclipse.stem.ui/src/org/eclipse/stem/ui/widgets/DecoratorSelector.java
@@ -364,8 +364,10 @@
 	 */
 	void initializeCombo(final Combo combo, final String[] names,
 			final int selectionIndex) {
-		combo.setItems(names);
-		combo.select(selectionIndex);
+		if(!combo.isDisposed()) {
+			combo.setItems(names);
+			combo.select(selectionIndex);
+		}
 	} // initializeCombo
 
 	/**