Well the problem is this file is I think 35MB plus so you can't upload it to something like virustotal which has a limit of 10MB, that is the usual way of confirming an FP.
In this case you either have to trust shockwave.com and the single scan by DrWeb finding it clean, pause the web shield to download, the standard shield will alert but you can choose ignore. But before you can run it to install the game you would have to exclude it from scans.
add it to the exclusions lists:
Standard Shield, Customize, Advanced, Add and
Program Settings, Exclusions
I have reported the link you gave as a possible false positive, so I would suggest you do the same. Send the above URL to virus@avast.com, a brief explanation of the problem, a link to this topic might help and false positive in the email subject.