Option to un-filter facet not shown for `?col__exact=value`

[simonw]

Spotted this on a page with COUNTY__exact=Lee in the URL:

With COUNTY=Lee you get this instead:

[simonw]

Relevant template:

datasette/datasette/templates/table.html

Lines 168 to 172 in e73fa72

	{% if not facet_value.selected %}
	<li><a href="{{ facet_value.toggle_url }}">{{ (facet_value.label | string()) or "-" }}</a> {{ "{:,}".format(facet_value.count) }}</li>
	{% else %}
	<li>{{ facet_value.label or "-" }} &middot; {{ "{:,}".format(facet_value.count) }} <a href="{{ facet_value.toggle_url }}" class="cross">&#x2716;</a></li>
	{% endif %}

Populated from here:

datasette/datasette/facets.py

Lines 246 to 253 in c496f2b

	column_qs = column
	if column.startswith("_"):
	column_qs = "{}__exact".format(column)
	selected = (column_qs, str(row["value"])) in qs_pairs
	if selected:
	toggle_path = path_with_removed_args(
	self.request, {column_qs: str(row["value"])}
	)

[simonw]

selected = (column_qs, str(row["value"])) in qs_pairs is wrong.