Make _DISABLE_FEED_BROWSER also disable the updateFeedBrowser RPC

The undocumented _DISABLE_FEED_BROWSER option added in commit
c39befacb2 turns off the UI for looking
at which feeds other users are subscribed to, but it did not prevent
you from manually constructing an RPC call to get the same data.  This
was a privacy risk for those who consider _DISABLE_FEED_BROWSER
important.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

classes/rpc.php

@@ -379,6 +379,8 @@ class RPC extends Handler_Protected {
 	}
 
 	function updateFeedBrowser() {
+		if (defined('_DISABLE_FEED_BROWSER') && _DISABLE_FEED_BROWSER) return;
+
 		$search = $this->dbh->escape_string($_REQUEST["search"]);
 		$limit = $this->dbh->escape_string($_REQUEST["limit"]);
 		$mode = (int) $this->dbh->escape_string($_REQUEST["mode"]);

include/feedbrowser.php

@@ -1,6 +1,8 @@
 <?php
 	function make_feed_browser($search, $limit, $mode = 1) {
 
+		if (defined('_DISABLE_FEED_BROWSER') && _DISABLE_FEED_BROWSER) return;
+
 		$owner_uid = $_SESSION["uid"];
 		$rv = '';