fix ErrorOnlyArchiver logging Error, also when there is none

ErrorOnlyArchiver.go

@@ -9,7 +9,9 @@ func NewErrorOnlyArchiver(conf *Config) func(string, error) {
 	return func(filePath string, archiveErr error) {
 		if archiveErr != nil {
 			err := writeErrorFile(conf, filePath, archiveErr)
-			logger.Error(err)
+			if err != nil {
+				logger.Error(err)
+			}
 		}
 	}
 }