Fix possible crashes on .unwrap()s

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

src/threads/data/backfill/news.rs

@@ -57,7 +57,7 @@ impl super::Handler for Handler {
     }
 
     async fn queue_backfill(&self, jobs: &HashMap<String, Job>) {
-        if *ALPACA_SOURCE == Source::Sip {
+        if jobs.is_empty() || *ALPACA_SOURCE == Source::Sip {
             return;
         }
 
@@ -71,6 +71,10 @@ impl super::Handler for Handler {
 
     #[allow(clippy::too_many_lines)]
     async fn backfill(&self, jobs: HashMap<String, Job>) {
+        if jobs.is_empty() {
+            return;
+        }
+
         let symbols = jobs.keys().cloned().collect::<Vec<_>>();
         let fetch_from = jobs.values().map(|job| job.fetch_from).min().unwrap();
         let fetch_to = jobs.values().map(|job| job.fetch_to).max().unwrap();