fix #2883

[sramazzina]

fix #2883 Workflow executor: do not fire consistency check in case there are no result from sub-workflows

I decided it was a better idea to relax the constraints and don't block the execution in case a field in the result stream was missing. This is because if that missing field(s) come from a sub-pipeline respectively called by the workflow's executor sub-workflow, that behavior could be unwanted in case the sub-pipeline does not return any rows (and so any new fields respect to the input result row). I think it would be a good idea to add a flag to re-enable the raise of an exception in case a field of the required results fields list is missing from the results fields list to support certain use-cases. Feel free to add an issue to request this and I will be more than happy to do that. Therefore, currently, the exception will be raised only if there's a difference in datatypes, same as in the original version but now more clean and complete.

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