No error code if connection is dropped

[JekRock]

I had the following bug. I sent two AGWriteDB requests and between these two requests the connection to plc was dropped (I've emulated this by disconnecting the network on PC). After the second request I didn't get any error but there was no data in DB. And after all following request the same.
I've found that the bug was in this line. Here the error message from this line should be returned, but it's kinda hidden by err variable from the writeArea function (I'm not an expert in Go, so I don't know how it has happened. I'll be gratefull if you explain this).
I've changed error variable name and it has solved the bug.
Please check the pull request #6