publish-calendar: Correct type of a 'port' variable to match GUri's port type

GUri uses -1 for 'port not set', but storing such value into an unsigned
variable makes the -1 an out of bounds value.

src/plugins/publish-calendar/url-editor-dialog.c

@@ -305,7 +305,7 @@ set_from_uri (UrlEditorDialog *dialog)
 	const gchar *user;
 	const gchar *host;
 	const gchar *path;
-	guint port;
+	gint port;
 
 	uri = dialog->uri;