Here is a minimal patch to add a User-Agent: header to outgoing requests.
I've tested it and found that it restored location search functionality.
I don't consider it a complete fix since it doesn't make the search URI
configurable.
Attempt a minimal fix for Debian #891325.
Index: git/panel-plugin/weather.c
===================================================================
--- git.orig/panel-plugin/weather.c 2018-02-24 17:08:19.734257691 +0100
+++ git/panel-plugin/weather.c 2018-02-24 18:04:11.807358994 +0100
@@ -1852,6 +1852,10 @@
g_object_set(data->session, SOUP_SESSION_TIMEOUT,
CONN_TIMEOUT, NULL);
+ /* Set the user agent to something sensible */
+ g_object_set(data->session, SOUP_SESSION_USER_AGENT,
+ PACKAGE_NAME "/" PACKAGE_VERSION " ", NULL);
+
/* Set the proxy URI from environment */
proxy_uri = g_getenv("HTTP_PROXY");
if (!proxy_uri)
