fix mistake of rethrowing exception (which loses call stack) to just throw (which does not)

server/AyaNova/util/FileUtil.cs

@@ -570,7 +570,7 @@ namespace AyaNova.Util
                 {
                     log.LogError(ex, $"FileUtil::BackupAttachments");
                 }
-                throw ex;
+                throw;
             }
         }