search: check for error in query_result before returning JSON

[GraemeWatt]

If search results are requested in JSON format, the current code tries to calculate query_result['hits'] and return the JSON results without checking if there is an error in the query_result:

hepdata/hepdata/modules/search/views.py

Lines 249 to 250 in 3dcdfe6

	query_result['hits'] = {'total': query_result['total']}
	return jsonify(query_result)

An invalid query like q=%27%5B0%5D gives an exception KeyError: 'total', e.g. Sentry event. A JSON error message should be returned instead.