Created attachment 174132 [details]
PromptDialog with long subtitle

I am unable to reproduce this using newest kirigami + kirigami-gallery

This is the prompt dialog code:

```qml

    Kirigami.PromptDialog {
        id: textPromptDialog
        title: "New Folder"
        subtitle: "Long subtitle aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"

        standardButtons: Kirigami.Dialog.NoButton
        customFooterActions: [
            Kirigami.Action {
                text: qsTr("Create Folder")
                icon.name: "dialog-ok"
                onTriggered: {
                    showPassiveNotification("Created");
                    textPromptDialog.close();
                }
            },
            Kirigami.Action {
                text: qsTr("Cancel")
                icon.name: "dialog-cancel"
                onTriggered: {
                    textPromptDialog.close();
                }
            }
        ]

        FormCard.FormTextFieldDelegate {
            label: qsTr("Folder name:")
            leftPadding: 0
            rightPadding: 0
        }
    }

```

It works as expected if the subtitle is known at creation time.

Minimal example to reproduce the problem:
```qml
    Kirigami.PromptDialog {
        id: textPromptDialog
        title: "Title"
        subtitle: "empty"
        Component.onCompleted: {
            subtitle = "A long subtitle which should change the width of the PromptDialog"
        }
    }
```

Created attachment 174134 [details]
Minimal example

(In reply to Plata from comment #2)
> It works as expected if the subtitle is known at creation time.
> 
> Minimal example to reproduce the problem:
> ```qml
>     Kirigami.PromptDialog {
>         id: textPromptDialog
>         title: "Title"
>         subtitle: "empty"
>         Component.onCompleted: {
>             subtitle = "A long subtitle which should change the width of the
> PromptDialog"
>         }
>     }
> ```

Thanks, i could repro it now!