Make input loading fallible in SyncFromDiskStage

Author: R9295

libafl/src/stages/sync.rs

@@ -75,7 +75,7 @@ impl<CB, E, EM, I, S, Z> Named for SyncFromDiskStage<CB, E, EM, I, S, Z> {
 
 impl<CB, E, EM, I, S, Z> Stage<E, EM, S, Z> for SyncFromDiskStage<CB, E, EM, I, S, Z>
 where
-    CB: FnMut(&mut Z, &mut S, &Path) -> Result<I, Error>,
+    CB: FnMut(&mut Z, &mut S, &Path) -> Result<Option<I>, Error>,
     Z: Evaluator<E, EM, I, S>,
     S: HasCorpus<I>
         + HasRand
@@ -134,6 +134,9 @@ where
                 .unwrap()
                 .left_to_sync
                 .retain(|p| p != &path);
+            let Some(input) = input else {
+                continue;
+            };
             log::debug!("Syncing and evaluating {path:?}");
             fuzzer.evaluate_input(state, executor, manager, &input)?;
         }