backupAndRestore: Possible restore-from-file fix for certain environments

`requestIdleCallbacks` gives the browser a little more time to retrieve data from the file selector window after it is closed.

Author: larsjohnsen

lib/modules/backupAndRestore/providers/File.js

@@ -25,8 +25,8 @@ export class File extends Provider {
 				reader.readAsText(file);
 			});
 			// There is no proper way to detect when a file dialog is closed.
-			// We must use setTimeout so that the change event fires first.
-			Promise.all([waitForEvent(window, 'mousemove'), waitForEvent(window, 'focus')]).then(() => setTimeout(() => {
+			// We must use requestIdleCallback so that the change event has time to fire first.
+			Promise.all([waitForEvent(window, 'mousemove'), waitForEvent(window, 'focus')]).then(() => requestIdleCallback(() => {
 				if (loading) return; // Reader has started loading
 				if (!link.files.length) reject(new Error('No file selected.'));
 			}));