download_strategy: more robust filename content encoding handling.
download_strategy: more robust filename content encoding handling.

Fixes #5713.

EricFromCanada/brew,konqui/brew,reitermarkus/brew,claui/brew,nandub/brew,sjackman/homebrew,EricFromCanada/brew,vitorgalvao/brew,sjackman/homebrew,MikeMcQuaid/brew,JCount/brew,reitermarkus/brew,sjackman/homebrew,nandub/brew,vitorgalvao/brew,Homebrew/brew,reitermarkus/brew,claui/brew,reitermarkus/brew,mahori/brew,MikeMcQuaid/brew,JCount/brew,EricFromCanada/brew,mahori/brew,Homebrew/brew,Homebrew/brew,mahori/brew,vitorgalvao/brew,konqui/brew,Homebrew/brew,konqui/brew,EricFromCanada/brew,sjackman/homebrew,MikeMcQuaid/brew,JCount/brew,nandub/brew,vitorgalvao/brew,konqui/brew,JCount/brew,mahori/brew,MikeMcQuaid/brew,nandub/brew,claui/brew,claui/brew