raft: remove a guard that is no longer necessary

raft/log.go

@@ -176,9 +176,7 @@ func (l *raftLog) appliedTo(i uint64) {
 }
 
 func (l *raftLog) stableTo(i uint64) {
-	if len(l.unstableEnts) > 0 {
-		l.unstableEnts = l.unstableEnts[i+1-l.unstable:]
-	}
+	l.unstableEnts = l.unstableEnts[i+1-l.unstable:]
 	l.unstable = i + 1
 }