Search: It should be possible to add a WMS layer as searchable without specifying any search fields

[jacobwod]

The problem

Currently, if we setup a WMS layer with the following search settings:

We'd get something like this in the call to the WMS service (please note the PropertyName, it's empty!):

<GetFeature
	xmlns="http://www.opengis.net/wfs" service="WFS" version="1.1.0" outputFormat="GML3" maxFeatures="100" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.1.0/wfs.xsd"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<Query typeName="op2050_a_vattendjup_vid_skyfall" srsName="EPSG:3008">
		<Filter
			xmlns="http://www.opengis.net/ogc">
			<PropertyIsLike wildCard="*" singleChar="." escapeChar="!" matchCase="false">
				<PropertyName></PropertyName>
				<Literal>stora*</Literal>
			</PropertyIsLike>
		</Filter>
	</Query>
</GetFeature>

The motivation

One use case is that we would like to make a WMS layer searchable using the spatial tools, but there is not need (or no data to search in!) regarding textual searches.

The solution

If no searchFields are defined but the geometry column is specified, we should only care about this layer for spatial searches.

[Hallbergs]

Very nice! Search sources only intended for spatial search are probably not that uncommon!