Remove document listener from *old* document on setDocument()

UpdateDocumentListener is added to document but not always removed in
ProjectionViewer, regression introduced by commit
1848058

This fixes remaining possible leak, where *multiple* documents were used
in ProjectionViewer.

See eclipse-jdt/eclipse.jdt.ui#2532

Author: iloveeclipse

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

@@ -400,6 +400,7 @@ public void setDocument(IDocument document, IAnnotationModel annotationModel, in
 		}
 
 		if (fProjectionAnnotationModel != null) {
+			removeDocumentUpdateListener();
 			wasProjectionEnabled= removeProjectionAnnotationModel(getVisualAnnotationModel()) != null;
 			fProjectionAnnotationModel= null;
 		}
@@ -413,6 +414,15 @@ public void setDocument(IDocument document, IAnnotationModel annotationModel, in
 
 	}
 
+	private void removeDocumentUpdateListener() {
+		if (fUpdateDocumentListener != null) {
+			IDocument document= getDocument();
+			if (document != null) {
+				document.removeDocumentListener(fUpdateDocumentListener);
+			}
+		}
+	}
+
 	@Override
 	protected IAnnotationModel createVisualAnnotationModel(IAnnotationModel annotationModel) {
 		IAnnotationModel model= super.createVisualAnnotationModel(annotationModel);
@@ -554,10 +564,7 @@ public final void disableProjection() {
 				super.setVisibleRegion(fVisibleRegionDuringProjection.getOffset(), fVisibleRegionDuringProjection.getLength());
 				fVisibleRegionDuringProjection= null;
 			}
-			IDocument document= getDocument();
-			if (document != null) {
-				document.removeDocumentListener(fUpdateDocumentListener);
-			}
+			removeDocumentUpdateListener();
 		}
 	}
 
@@ -1480,12 +1487,7 @@ private boolean willAutoExpand(Position position, int offset, int length) {
 	@Override
 	protected void handleDispose() {
 		fWasProjectionEnabled= false;
-		if (fUpdateDocumentListener != null) {
-			IDocument document= getDocument();
-			if (document != null) {
-				document.removeDocumentListener(fUpdateDocumentListener);
-			}
-		}
+		removeDocumentUpdateListener();
 		super.handleDispose();
 	}