Google App Engine rule breaks sound in Flash game "Realm of the Mad God" #9667

Affected URL: http://www.realmofthemadgod.com/

Tested in Firefox 53.0 with Adobe Flash 25 on Ubuntu 16.10.

While sound can be turned on and off in the game settings, this rule prevents sound from being played even if it is switched on (the same game issue has previously been traced to players using certain web proxies, so I assume that it has something to do with specific web requests failing).