Don't use Display.syncExec() for refresh in RuntimeClasspathViewer

The listener may be called from a background thread that already holds
some locks. To refresh RuntimeClasspathViewer UI in the current case,
syncExec is not needed, asyncExec is enough and it would not acquire the
UI lock from an unknown thread.

Fixes #672

Author: iloveeclipse

org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/classpath/RuntimeClasspathViewer.java

@@ -64,17 +64,7 @@ public class RuntimeClasspathViewer implements IClasspathViewer {
 
 		@Override
 		public void preferenceChange(PreferenceChangeEvent event) {
-			if (DebugUIPlugin.getStandardDisplay().getThread().equals(Thread.currentThread())) {
-				refresh(true);
-			} else {
-				DebugUIPlugin.getStandardDisplay().syncExec(new Runnable() {
-					@Override
-					public void run() {
-						refresh(true);
-					}
-				});
-			}
-
+			DebugUIPlugin.getStandardDisplay().asyncExec(() -> refresh(true));
 		}
 	};
 
@@ -395,6 +385,9 @@ public void setSelection(ISelection selection) {
 
 	@Override
 	public void refresh(Object entry) {
+		if (fTree.isDisposed()) {
+			return;
+		}
 		getTreeViewer().refresh();
 	}