Poor error message for empty subset

[jonescc]

To reproduce

Submit a subset request selecting no data (I specified an end time before the start time accidentally)

What happens

<ns3:ExecuteResponse statusLocation="https://s3-ap-southeast-2.amazonaws.com/aws-wps-dev-testing/jobs/a0c7d186-d89b-4154-bddd-f721c323b6c4/status.xml" service="WPS" version="1.0.0" xml:lang="en-US" xmlns:ns2="http://www.w3.org/1999/xlink" xmlns:ns1="http://www.opengis.net/ows/1.1" xmlns:ns3="http://www.opengis.net/wps/1.0.0">
  <ns3:Status creationTime="2017-11-01T22:20:45.621Z">
    <ns3:ProcessFailed>
      <ns1:ExceptionReport version="1.0.0">
        <ns1:Exception exceptionCode="AggregationError">
          <ns1:ExceptionText>Exception occurred during aggregation :Could not convert output to csv: 'java.io.EOFException: Reading /tmp/agg2577211535447471107.nc at 0 file length = 0'</ns1:ExceptionText>
        </ns1:Exception>
      </ns1:ExceptionReport>
    </ns3:ProcessFailed>
  </ns3:Status>
</ns3:ExecuteResponse>

What I expect to happen

Get an error message saying end time cannot be before start time - or your subset selected no data or something along those lines.

[bhasin85]

Agree. We should improve the error message. However, I don't think the portal UI allows you to do that.

[jonescc]

Needs to be fixed in the request handler

[jonescc]

For wps clients like MARVL

[ccmoloney]

We should add validation like this to this PR: #215

[pmbohm]

relates to https://github.com/aodn/issues/issues/445

[pmbohm]

relates to #266