ui: TapeRestore: mark datastore selector as 'not a form field'

since extjs 7.0 those will get picked up by our query logic and
sent to the backend. prevent that by setting isFormField to false
(we assemble the values differently)

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

www/tape/window/TapeRestore.js

@@ -567,6 +567,7 @@ Ext.define('PBS.TapeManagement.DataStoreMappingGrid', {
 	    flex: 1,
 	    widget: {
 		xtype: 'pbsDataStoreSelector',
+		isFormField: false,
 		allowBlank: true,
 		bind: {
 		    emptyText: '{emptyMeans}',