Use Math.round() instead of Math.floor() when determining page of attachments to query in wp.media.model.Query.sync.

This was causing an infinite loop of AJAX requests - so.... good catch!

Props Veritaserum.
Fixes #31116.

Built from https://develop.svn.wordpress.org/trunk@31406


git-svn-id: http://core.svn.wordpress.org/trunk@31387 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-alpha-31405';
+$wp_version = '4.2-alpha-31406';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.