Support combination of empty DB geometry and any other QML geometry

[jirik]

version: 1.13.2

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/celery/app/trace.py", line 412, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/code/src/layman/make_celery.py", line 36, in __call__
    return self.run(*args, **kwargs)
  File "/code/src/layman/layer/qgis/tasks.py", line 29, in refresh_wms
    wms.save_qgs_file(username, layername)
  File "/code/src/layman/layer/qgis/wms.py", line 70, in save_qgs_file
    source_type = util.get_source_type(db_types, qml_geometry)
  File "/code/src/layman/layer/qgis/util.py", line 200, in get_source_type
    data=f'Unknown combination of QML geometry "{qml_geometry}" and DB geometry types '
layman.http.LaymanError: LaymanError code=47 message=Error in QML data=Unknown combination of QML geometry "Point" and DB geometry types [] private_info=None