[CLIENT] Client black-screens if Documents location doesn't exist (though doesn't use it)

This appears to be the general root cause of the bug discussed below (see my comment therein): http://boards.na.leagueoflegends.com/en/c/bug-report/VYxE4a6B-client-login-screen-blank-after-hitting-launch

If the Windows Documents location doesn't include a valid (existing) folder, the LoL client is a plain black screen after hitting Launch and there is no way of launching LoL. This is easy to reproduce:

-- create a folder C:\TempDocs -- change the location of the Windows Documents location to be that folder -- delete that folder (whilst navigating C: where it will now shows as 'named' Documents) -- launch the LoL client (black-screens) -- reset the Documents location back to the correct folder (LoL client launches correctly again)

It looks like LoL doesn't store anything in the Documents location (even in hidden folders), so it should not be affected by such issues. (If it does use it in some circumstances, there should be a clear error message that this is the problem on launching the client. I suspect it is some hidden requirement of Adobe Air or similar.)

Raising as a separate bug to highlight what looks like the root cause, and to check that this is addressed in the new Alpha client (and/or potentially fixed in the current client).