Fall back to filename in backup creation notification if path not available

(cherry picked from commit 6b9180844deee00b23a60a8f265110716754876e)

app/src/main/java/eu/kanade/tachiyomi/data/backup/BackupNotifier.kt

@@ -68,6 +68,8 @@ class BackupNotifier(private val context: Context) {
 
             if (unifile.filePath != null) {
                 setContentText(unifile.filePath)
+            } else {
+                setContentText(unifile.name)
             }
 
             // Clear old actions if they exist