fix 2

Author: stanislav-tkach

rust/cardano-chain-follower/examples/follow_chains.rs

@@ -96,7 +96,11 @@ async fn start_sync_for(network: &Network, matches: ArgMatches) -> Result<(), Bo
     let mithril_dl_workers = format!("{}", dl_config.workers);
 
     if let Some(chunk_size) = matches.get_one::<u16>("mithril-sync-chunk-size") {
-        dl_config = dl_config.with_chunk_size(*chunk_size as usize * 1024 * 1024);
+        let chunk_size = chunk_size
+            .checked_mul(1024)
+            .and_then(|v| v.checked_mul(1024))
+            .ok_or_else(|| "Chunk size overflow")?;
+        dl_config = dl_config.with_chunk_size(chunk_size);
     }
     let mithril_dl_chunk_size = format!("{} MBytes", dl_config.chunk_size / (1024 * 1024));