Bug 11814 OpenExternalJavadoc action should not call findElement on JAR
This causes an exception: Java Model Exception: Java Model Status [Invalid path: C:/Java/IBM1.3/jre/lib/rt.jar.] at org.eclipse.jdt.internal.core.JavaProject.findElement(JavaProject.java:435) at org.eclipse.jdt.internal.ui.actions.OpenExternalJavadocAction.run(OpenExternalJavadocAction.java:102) at org.eclipse.ui.texteditor.RetargetTextEditorAction.run(RetargetTextEditorAction.java:103) at org.eclipse.jface.action.Action.runWithEvent(Action.java:473) at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:407) at org.eclipse.jface.action.ActionContributionItem.handleWidgetEvent(ActionContributionItem.java(Compiled Code)) at org.eclipse.jface.action.ActionContributionItem$ActionListener.handleEvent(ActionContributionItem.java(Compiled Code)) at org.eclipse.jface.action.ActionContributionItem$ActionListener.handleEvent(ActionContributionItem.java(Compiled Code)) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java(Compiled Code)) at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java(Compiled Code)) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java(Compiled Code)) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java(Compiled Code)) at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java(Compiled Code)) at org.eclipse.ui.internal.Workbench.run(Workbench.java:698) at org.eclipse.core.internal.boot.InternalBootLoader.run(InternalBootLoader.java:777) at org.eclipse.core.boot.BootLoader.run(BootLoader.java:319) at java.lang.reflect.Method.invoke(Native Method) at org.eclipse.core.launcher.Main.basicRun(Main.java:196) at org.eclipse.core.launcher.Main.run(Main.java:555) at org.eclipse.core.launcher.UIMain.main(UIMain.java:52) 4 org.eclipse.jdt.core 979 Invalid path: C:/Java/IBM1.3/jre/lib/rt.jar.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
return null;
		}
		if (path.isEmpty()) {
			return new Path(varName);
		}
		
		IPath varPath= JavaCore.getClasspathVariable(varName);
		if (varPath != null) {
			if (varPath.isPrefixOf(path)) {
				path= path.removeFirstSegments(varPath.segmentCount());
			} else {
				path= new Path(path.lastSegment());
			}
		} else {
			path= new Path(path.lastSegment());
		}
		return new Path(varName).append(path);
	}
	
	/**
	 * Creates a runnable that sets the source attachment by modifying the project's classpath.
	 */
	public IRunnableWithProgress getRunnable(final IJavaProject jproject, final Shell shell) {
		return new IRunnableWithProgress() {
			public void run(IProgressMonitor monitor) throws InvocationTargetException {				
				try {
					boolean isExported= fOldEntry != null ? fOldEntry.isExported() : false;
					IClasspathEntry newEntry;
					if (fIsVariableEntry) {
						newEntry= JavaCore.newVariableEntry(fJARPath, getSourceAttachmentPath(), getSourceAttachmentRootPath(), isExported);