Fix support for flatpak FileChooser portal

FileChooser portal expects filter property in a(sa(us)) format but by
default, using enum, we will end up with a(sa(is)), thus we have to
specify format for the enum.

Change-Id: I7de971197a0c77d6dca092edda7d428d90394574
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/platformthemes/flatpak/qflatpakfiledialog_p.h

@@ -51,7 +51,7 @@ class QFlatpakFileDialog : public QPlatformFileDialogHelper
     Q_OBJECT
     Q_DECLARE_PRIVATE(QFlatpakFileDialog)
 public:
-    enum ConditionType {
+    enum ConditionType : uint {
         GlobalPattern = 0,
         MimeType = 1
     };