fts-solr: Append '/' to URL path when missing in configuration

This fixes a crash when url parameter has empty path like
http://localhost:8080 instead of http://localhost:8080/ and makes using
url like http://localhost:8080/solr behave the same as
http://localhost:8080/solr/

src/plugins/fts-solr/solr-connection.c

@@ -101,6 +101,20 @@ static int solr_xml_parse(struct solr_connection *conn,
 	return 0;
 }
 
+/* Regardless of the specified URL, make sure path ends in '/' */
+static char *solr_connection_create_http_base_url(struct http_url *http_url)
+{
+	if (http_url->path == NULL)
+		return i_strconcat("/", http_url->enc_query, NULL);
+	size_t len = strlen(http_url->path);
+	if (len > 0 && http_url->path[len-1] != '/')
+		return i_strconcat(http_url->path, "/",
+				   http_url->enc_query, NULL);
+	/* http_url->path is NULL on empty path, so this is impossible. */
+	i_assert(len != 0);
+	return i_strconcat(http_url->path, http_url->enc_query, NULL);
+}
+
 int solr_connection_init(const char *url,
 			 const struct ssl_iostream_settings *ssl_client_set,
 			 bool debug, struct solr_connection **conn_r,
@@ -121,7 +135,7 @@ int solr_connection_init(const char *url,
 	conn = i_new(struct solr_connection, 1);
 	conn->http_host = i_strdup(http_url->host.name);
 	conn->http_port = http_url->port;
-	conn->http_base_url = i_strconcat(http_url->path, http_url->enc_query, NULL);
+	conn->http_base_url = solr_connection_create_http_base_url(http_url);
 	conn->http_ssl = http_url->have_ssl;
 	if (http_url->user != NULL) {
 		conn->http_user = i_strdup(http_url->user);