apply 0b2243acf0 on mvcc

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-mvcc/src/lsm_iterator.rs

@@ -136,14 +136,14 @@ impl<I: StorageIterator> StorageIterator for FusedIterator<I> {
     }
 
     fn key(&self) -> Self::KeyType<'_> {
-        if self.has_errored || !self.iter.is_valid() {
+        if !self.is_valid() {
             panic!("invalid access to the underlying iterator");
         }
         self.iter.key()
     }
 
     fn value(&self) -> &[u8] {
-        if self.has_errored || !self.iter.is_valid() {
+        if !self.is_valid() {
             panic!("invalid access to the underlying iterator");
         }
         self.iter.value()