feature: validate term value

src/raft.rs

@@ -380,6 +380,9 @@ impl<T: Storage> Raft<T> {
         if raft_state.hard_state != HardState::default() {
             r.load_state(&raft_state.hard_state);
         }
+        if r.term == 0 {
+            fatal!(r.logger, "Invalid term value: 0");
+        }
         if c.applied > 0 {
             r.commit_apply(c.applied);
         }

src/storage.rs

@@ -419,6 +419,8 @@ impl MemStorage {
         // In practice, we choose the second way by assigning non-zero index to first index. Here
         // we choose the first way for historical reason and easier to write tests.
         core.raft_state.conf_state = ConfState::from(conf_state);
+        // Initialize term with a valid value (anything except 0)
+        core.raft_state.hard_state.term = 1;
     }
 
     /// Opens up a read lock on the storage and returns a guard handle. Use this