Add a default back to INFOPATH
Add a default back to INFOPATH

It looks like #7738 removed the default unintentionally. This adds it back. 

For scripts that `set -u`, this will fail if $INFOPATH is not already set (`INFOPATH: unbound variable`). This provides an empty default, but one that will still satisfy the trailing colon requirement.
sjackman/homebrew,reitermarkus/brew,reitermarkus/brew,Homebrew/brew,mahori/brew,vitorgalvao/brew,JCount/brew,Homebrew/brew,mahori/brew,reitermarkus/brew,EricFromCanada/brew,MikeMcQuaid/brew,mahori/brew,EricFromCanada/brew,MikeMcQuaid/brew,reitermarkus/brew,mahori/brew,JCount/brew,sjackman/homebrew,sjackman/homebrew,claui/brew,konqui/brew,EricFromCanada/brew,vitorgalvao/brew,konqui/brew,vitorgalvao/brew,MikeMcQuaid/brew,sjackman/homebrew,MikeMcQuaid/brew,konqui/brew,nandub/brew,nandub/brew,JCount/brew,claui/brew,EricFromCanada/brew,vitorgalvao/brew,konqui/brew,claui/brew,Homebrew/brew,nandub/brew,JCount/brew,claui/brew,Homebrew/brew,nandub/brew