Better exception handling if the WFS server is providing complex features

[qgib]

Author Name: Juergen Weichand (@JuergenWeichand)
Original Redmine Issue: 14686
Affected QGIS version: master
Redmine category:web_services_clients/wfs

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I've also did some testing with WFS 2.0 server providing complex features, which are not supported.

In the first case, the QGIS WFS provider is not able to parse the complex schema structure and returns the following message DescribeFeatureType failed for url srsname='EPSG:4326' typename='ad:Address' url='http://demo.deegree.org/inspire-workspace/services/wfs' version='2.0.0' table="" sql=: failed retrieving attributes from schema.
http://demo.deegree.org/inspire-workspace/services/wfs

In the second case, the layer is containing null values and is non spatial.
http://services.cuzk.cz/wfs/inspire-cp-wfs.asp

Please also refer to:
#2977 (comment)
#2977 (comment)

[qgib]

Author Name: Even Rouault (@rouault)

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A more explicit error message is given now.

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• status_id was changed from Open to Closed