GuestMemorySliceIterator: clarify error case for .stop_on_error()

Author: bonzini

src/guest_memory.rs

@@ -539,6 +539,7 @@ impl<'a, M: GuestMemory + ?Sized> GuestMemorySliceIterator<'a, M> {
 
     /// Adapts this [`GuestMemorySliceIterator`] to return `None` (e.g. gracefully terminate)
     /// when if encounters an error after successfully producing at least one slice.
+    /// Return an error if requesting the first slice returns an error.
     pub fn stop_on_error(self) -> Result<impl Iterator<Item = VolatileSlice<'a, MS<'a, M>>>> {
         let mut peek = self.peekable();
         if let Some(err) = peek.next_if(Result::is_err) {