put success with TTL=-1, but TTL value is null in tikv, should restrict ttl value >=0

[seiya-annie]

1. step
   @test
   public void putwithInvalidTTL() {
   if (!initialized) return;
   long ttl = -1;
   ByteString key = ByteString.copyFromUtf8("key_lt");
   ByteString value = ByteString.copyFromUtf8("value1");
   checkDelete(key);
   try {
   client.put(key, value, ttl);
   } catch (Exception e) {
   logger.info("put fail for error:" + e);
   }
   Long t = client.getKeyTTL(key);
   logger.info("current ttl of key is " + t);
   checkDelete(key);
   logger.info("done");
   }

2. expect result:
   put fail with invalid ttl value

3. current result:
   put successfully, and get back value is null.