Fix for apps that will change env['PATH_INFO']

[gaganawhad]

problem: So I am using font_assets along with sidekiq and it seems that sidekiq's web interface is changing the value of env['PATH_INFO'] to a blank string, which then breaks things.

caveat: I am not at expert at RACK so I am not sure that this fixes the problem at the root. Also, I am not really sure if sidekiq should be changing the env.

This is a first attempt at a fix. The test suite passes. I am not sure if you want to add a test case for apps that change the env, so I didn't add one.

Another possible fix might be to allow for env['PATH_INFO'] to hold a blank string but then again, I am not exactly sure what exactly the culprit is.

[ericallam]

I just merged another patch that I think should solve this issue too. If you get a chance could you test it out and report back?

[jjb]

i had this problem too, described here sidekiq/sidekiq#1514

the problem goes away with 01861d9