Fix self.iterations underflow (#1942)

* fix

* fix

* FMT

libafl/src/stages/mutational.rs

@@ -109,7 +109,11 @@ where
         manager: &mut EM,
     ) -> Result<(), Error> {
         start_timer!(state);
-        let num = self.iterations(state)? - self.execs_since_progress_start(state)?;
+
+        // Here saturating_sub is needed as self.iterations() might be actually smaller than the previous value before reset.
+        let num = self
+            .iterations(state)?
+            .saturating_sub(self.execs_since_progress_start(state)?);
         let mut testcase = state.current_testcase_mut()?;
 
         let Ok(input) = I::try_transform_from(&mut testcase, state) else {

libafl/src/stages/tuneable.rs

@@ -222,7 +222,9 @@ where
             }
             (None, None) => {
                 // fall back to random
-                let iters = self.iterations(state)? - self.execs_since_progress_start(state)?;
+                let iters = self
+                    .iterations(state)?
+                    .saturating_sub(self.execs_since_progress_start(state)?);
                 for _ in 1..=iters {
                     self.perform_mutation(fuzzer, executor, state, manager, &input)?;
                 }