Disable menuItems if they aren't visible

This prevents the shortcuts from breaking

resources/qml/Menus/FileMenu.qml

@@ -25,6 +25,7 @@ Cura.Menu
         id: openMenu
         action: Cura.Actions.open
         visible: base.fileProviderModel.count == 1
+        enabled: base.fileProviderModel.count == 1
     }
 
     OpenFilesMenu
@@ -42,7 +43,7 @@ Cura.Menu
         shortcut: StandardKey.Save
         text: catalog.i18nc("@title:menu menubar:file", "&Save Project...")
         visible: saveProjectMenu.model.count == 1
-        enabled: UM.WorkspaceFileHandler.enabled
+        enabled: UM.WorkspaceFileHandler.enabled && saveProjectMenu.model.count == 1
         onTriggered:
         {
             var args = { "filter_by_machine": false, "file_type": "workspace", "preferred_mimetypes": "application/vnd.ms-package.3dmanufacturing-3dmodel+xml" };

resources/qml/Menus/SaveProjectMenu.qml

@@ -41,6 +41,7 @@ Cura.Menu
                 }
             }
             shortcut: model.shortcut
+            enabled: saveProjectMenu.shouldBeVisible
         }
         onObjectAdded: saveProjectMenu.insertItem(index, object)
         onObjectRemoved: saveProjectMenu.removeItem(object)