Fix mariadb dump logic on unchanged database

src/symbols/mariadb/dump.rs

@@ -36,7 +36,7 @@ impl<N: AsRef<str>, C: CommandRunner, S: Storage> Symbol for Dump<'_, N, C, S> {
     let dump_date = self.storage.recent_date()?;
     let output = self.run_sql(&format!("select UNIX_TIMESTAMP(MAX(UPDATE_TIME)) from information_schema.tables WHERE table_schema = '{}'", self.db_name.as_ref())).await?;
     let modified_date = output.trim_end();
-    Ok(modified_date != "NULL" && u64::from_str(modified_date)? <= dump_date)
+    Ok(modified_date == "NULL" || u64::from_str(modified_date)? <= dump_date)
   }
 
   async fn execute(&self) -> Result<(), Box<dyn Error>> {