Update the era with the value in current block's state

At `on_term_close`, the term_common_params is not updated to the
new parameters yet. But the parameters in the current block's
state is updated, so we should get the `era` from there.

core/src/consensus/tendermint/engine.rs

@@ -246,7 +246,7 @@ impl ConsensusEngine for Tendermint {
 
         match term {
             0 => {}
-            _ => match term_common_params.expect("Term common params should exist").era() {
+            _ => match metadata.params().map_or(0, |p| p.era()) {
                 0 => {}
                 1 => block.state_mut().snapshot_term_params()?,
                 _ => unimplemented!("It is not decided how we handle this"),