Author: David Monllao
MDL-59786 analytics: Discard invalid samples
http://git.moodle.org/gw?p=moodle.git;a=commit;h=1a5204a42777d24cddd4663585bc0cb7b88df7d6
http://github.com/moodle/moodle/commit/1a5204a42777d24cddd4663585bc0cb7b88df7d6
+ 3.4 en [errorendbeforestart,core_analytics]