Improve performance for large selection

In a custom RCP application I noticed that selecting a huge amount of
files (by holding Shift-Scroll down for some seconds) gets slower with
the growing size of the selection.

We should short-circuit the evaluation the moment the overall result is
known to be false.

bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/actions/CommonActionProviderDescriptor.java

@@ -236,6 +236,7 @@ public boolean isEnabledFor(IStructuredSelection aStructuredSelection) {
 				context.setAllowPluginActivation(true);
 				if (NavigatorPlugin.safeEvaluate(enablement, context) != EvaluationResult.TRUE) {
 					isEnabled = false;
+					break;
 				}
 			}
 			if (!isEnabled) {