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/internal/findandreplace/overlay/FindReplaceOverlay.java

@@ -813,6 +813,10 @@ private void repositionTextSelection() {
 	}
 
 	private void positionToPart() {
+		if (isInvalidTargetShell()) {
+			close();
+			return;
+		}
 		getShell().requestLayout();
 		if (!(targetPart instanceof StatusTextEditor textEditor)) {
 			return;
@@ -833,6 +837,17 @@ private void positionToPart() {
 		repositionTextSelection();
 	}
 
+	private boolean isInvalidTargetPart() {
+		return targetPart == null || targetPart.getSite() == null || targetPart.getSite().getShell() == null;
+	}
+
+	private boolean isInvalidTargetShell() {
+		if (isInvalidTargetPart()) {
+			return false;
+		}
+		return getShell() == null || !targetPart.getSite().getShell().equals(getShell().getParent());
+	}
+
 	private Rectangle calculateAbsoluteControlBounds(Control control) {
 		Rectangle localControlBounds = control.getBounds();
 		int width = localControlBounds.width;

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

@@ -412,7 +412,7 @@ private void showDialog() {
 	}
 
 	private void showOverlayInEditor() {
-		if (overlay == null) {
+		if (shouldCreateNewOverlay()) {
 			Shell shellToUse = null;
 
 			if (fShell == null) {
@@ -431,6 +431,10 @@ private void showOverlayInEditor() {
 		overlay.getShell().addDisposeListener(__ -> removeDialogPreferenceListener());
 	}
 
+	private boolean shouldCreateNewOverlay() {
+		return overlay == null || overlay.getShell() == null || overlay.getShell().isDisposed();
+	}
+
 	@Override
 	public void update() {