Bug 570587 - Increase performance of refactorings

Unnecessary loss of performance caused by Bug 436581.

With change
https://git.eclipse.org/r/c/equinox/rt.equinox.bundles/+/175187
there is another option available how to fix this.

Change-Id: I66d75c4d516447735a05d76ef16b7edd5c4b6566
Signed-off-by: Carsten Hammer <carsten.hammer@t-online.de>
diff --git a/org.eclipse.jdt.core.manipulation/refactoring/org/eclipse/jdt/core/refactoring/CompilationUnitChange.java b/org.eclipse.jdt.core.manipulation/refactoring/org/eclipse/jdt/core/refactoring/CompilationUnitChange.java
index 78bb13d..604e31b 100644
--- a/org.eclipse.jdt.core.manipulation/refactoring/org/eclipse/jdt/core/refactoring/CompilationUnitChange.java
+++ b/org.eclipse.jdt.core.manipulation/refactoring/org/eclipse/jdt/core/refactoring/CompilationUnitChange.java
@@ -81,7 +81,7 @@
 	protected IDocument acquireDocument(IProgressMonitor pm) throws CoreException {
 		SubMonitor subMonitor= SubMonitor.convert(pm, 2);
 		fCUnit.becomeWorkingCopy(subMonitor.split(1));
-		Assert.isTrue(fCUnit.isWorkingCopy(), fCUnit.toString());
+		Assert.isTrue(fCUnit.isWorkingCopy(), !fCUnit.isWorkingCopy()?fCUnit.toString():""); //$NON-NLS-1$
 		return super.acquireDocument(subMonitor.split(1));
 	}