create-snapshot check if snapshot slot exists (#27153)

ledger-tool/src/main.rs

@@ -2817,6 +2817,11 @@ fn main() {
                     value_t_or_exit!(arg_matches, "snapshot_slot", Slot)
                 };
 
+                assert!(
+                    blockstore.meta(snapshot_slot).unwrap().is_some(),
+                    "snapshot slot doesn't exist"
+                );
+
                 let ending_slot = if is_minimized {
                     let ending_slot = value_t_or_exit!(arg_matches, "ending_slot", Slot);
                     if ending_slot <= snapshot_slot {