Fix icon being ignored in message action buttons

CURA-8112

resources/qml/Cura.qml

@@ -417,6 +417,7 @@ UM.MainWindow
                     Cura.PrimaryButton
                     {
                         text: model.name
+                        iconSource: UM.Theme.getIcon(model.icon)
                         height: UM.Theme.getSize("message_action_button").height
                     }
                 }
@@ -426,6 +427,7 @@ UM.MainWindow
                     Cura.SecondaryButton
                     {
                         text: model.name
+                        iconSource: UM.Theme.getIcon(model.icon)
                         height: UM.Theme.getSize("message_action_button").height
                     }
                 }
@@ -434,6 +436,11 @@ UM.MainWindow
                     Cura.TertiaryButton
                     {
                         text: model.name
+                        iconSource: {
+                            if (model.icon == null || model.icon == "")
+                                return UM.Theme.getIcon("LinkExternal")
+                            return UM.Theme.getIcon(model.icon)
+                        }
                         height: UM.Theme.getSize("message_action_button").height
                     }
                 }