Fix issue when trying to save multiple Records contain invalid data

Hi,

I got a problem with Salesforce Soap-Client, I'm trying to update many records in one foreach loop, when one of this records has invalid or missing data it throw <code>Phpforce\SoapClient\Exception\SaveException</code>.
For my case I catch it and I trying to update the second one but I have always the same error because in BulkSaver each array contain records getting empty after calling successfully each CRUD function.

I make this PR to fix this issue and I hope it begin merged soon.

Thanks!