query: Do not alter prefix in for-loop

I found this bug while I'm trying to use [SendMessageBatch in SQS](http://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_SendMessageBatch.html).

## Question

SQS still returns 400 with this fix because flattened attributes includes `.member.` in its prefix.

### Expected

```
Action=SendMessageBatch
QueueUrl=<snip>
SendMessageBatchRequestEntry.1.Id=msg-0
SendMessageBatchRequestEntry.1.MessageAttributes.1.Name=ATTR1
SendMessageBatchRequestEntry.1.MessageAttributes.1.Value.DataType=String
SendMessageBatchRequestEntry.1.MessageAttributes.1.Value.StringValue=STRING%21%21
SendMessageBatchRequestEntry.1.MessageAttributes.2.Name=ATTR2
SendMessageBatchRequestEntry.1.MessageAttributes.2.Value.DataType=Number
SendMessageBatchRequestEntry.1.MessageAttributes.2.Value.StringValue=12345
SendMessageBatchRequestEntry.1.MessageBody=body1
SendMessageBatchRequestEntry.2.Id=msg-1
SendMessageBatchRequestEntry.2.MessageAttributes.1.Name=ATTR1
SendMessageBatchRequestEntry.2.MessageAttributes.1.Value.DataType=String
SendMessageBatchRequestEntry.2.MessageAttributes.1.Value.StringValue=STRING%21%21
SendMessageBatchRequestEntry.2.MessageAttributes.2.Name=ATTR2
SendMessageBatchRequestEntry.2.MessageAttributes.2.Value.DataType=Number
SendMessageBatchRequestEntry.2.MessageAttributes.2.Value.StringValue=12345
SendMessageBatchRequestEntry.2.MessageBody=body2
Version=2012-11-05
```

### Actual (with this fix)

```
Action=SendMessageBatch
QueueUrl=<snip>
SendMessageBatchRequestEntry.member.1.Id=msg-0
SendMessageBatchRequestEntry.member.1.MessageAttributes.1.Name=ATTR1
SendMessageBatchRequestEntry.member.1.MessageAttributes.1.Value.DataType=String
SendMessageBatchRequestEntry.member.1.MessageAttributes.1.Value.StringValue=STRING%21%21
SendMessageBatchRequestEntry.member.1.MessageAttributes.2.Name=ATTR2
SendMessageBatchRequestEntry.member.1.MessageAttributes.2.Value.DataType=Number
SendMessageBatchRequestEntry.member.1.MessageAttributes.2.Value.StringValue=12345
SendMessageBatchRequestEntry.member.1.MessageBody=body1
SendMessageBatchRequestEntry.member.2.Id=msg-1
SendMessageBatchRequestEntry.member.2.MessageAttributes.1.Name=ATTR1
SendMessageBatchRequestEntry.member.2.MessageAttributes.1.Value.DataType=String
SendMessageBatchRequestEntry.member.2.MessageAttributes.1.Value.StringValue=STRING%21%21
SendMessageBatchRequestEntry.member.2.MessageAttributes.2.Name=ATTR2
SendMessageBatchRequestEntry.member.2.MessageAttributes.2.Value.DataType=Number
SendMessageBatchRequestEntry.member.2.MessageAttributes.2.Value.StringValue=12345
SendMessageBatchRequestEntry.member.2.MessageBody=body2
Version=2012-11-05
```