ProjectionAnnotationModel.expandAll should tolerate the empty selection

- ITextSelection.emptySelection has offset and length -1 so those values
need to be tolerated downstream, included in the recent-optimized
ProjectionAnnotationModel.expandAll method.

eclipse-platform#2257

bundles/org.eclipse.jface.text/projection/org/eclipse/jface/text/source/projection/ProjectionAnnotationModel.java

@@ -147,6 +147,10 @@ public boolean collapseAll(int offset, int length) {
 	 */
 	protected boolean expandAll(int offset, int length, boolean fireModelChanged) {
 
+		if (offset < 0 || length < 0) {
+			return false;
+		}
+
 		boolean expanding= false;
 
 		Iterator<Annotation> iterator= getAnnotationIterator(offset, length, true, true);