Find/Replace overlay: handle the case when moving editor between windows

When moving the targeted editor between different windows, the overlay
is closed to allow a retargetting.

fixes #1945

bundles/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/texteditor/FindReplaceAction.java

@@ -411,7 +411,7 @@ private void showDialog() {
 	}
 
 	private void showOverlayInEditor() {
-		if (overlay == null) {
+		if (overlay == null || !overlay.isOverlayOpen()) {
 			Shell shellToUse = null;
 
 			if (fShell == null) {

bundles/org.eclipse.ui.workbench.texteditor/src/org/eclipse/ui/texteditor/FindReplaceOverlay.java

@@ -763,6 +763,10 @@ private void repositionTextSelection() {
 	}
 
 	private void positionToPart() {
+		if (!targetPart.getSite().getShell().equals(getShell().getParent())) {
+			close();
+			return;
+		}
 		getShell().requestLayout();
 		if (!(targetPart instanceof StatusTextEditor)) {
 			return;
@@ -863,4 +867,8 @@ private static boolean okayToUse(Widget widget) {
 	public void setPositionToTop(boolean shouldPositionOverlayOnTop) {
 		positionAtTop = shouldPositionOverlayOnTop;
 	}
+
+	public boolean isOverlayOpen() {
+		return overlayOpen;
+	}
 }