curl: handle more non-executable curl edge-cases.
curl: handle more non-executable curl edge-cases.

Address some additional issues mentioned in #3624.

JCount/brew,JCount/brew,MikeMcQuaid/brew,ilovezfs/brew,Homebrew/brew,JCount/brew,JCount/brew,nandub/brew,mgrimes/brew,mgrimes/brew,pseudocody/brew,nandub/brew,Homebrew/brew,konqui/brew,maxim-belkin/brew,mahori/brew,sjackman/homebrew,reelsense/brew,DomT4/brew,hanxue/linuxbrew,vitorgalvao/brew,EricFromCanada/brew,sjackman/homebrew,konqui/brew,konqui/brew,hanxue/linuxbrew,nandub/brew,vitorgalvao/brew,vitorgalvao/brew,hanxue/linuxbrew,alyssais/brew,EricFromCanada/brew,sjackman/homebrew,Homebrew/brew,mgrimes/brew,maxim-belkin/brew,reitermarkus/brew,EricFromCanada/brew,mahori/brew,claui/brew,nandub/brew,Linuxbrew/brew,alyssais/brew,reitermarkus/brew,ilovezfs/brew,Linuxbrew/brew,MikeMcQuaid/brew,claui/brew,mahori/brew,alyssais/brew,vitorgalvao/brew,DomT4/brew,MikeMcQuaid/brew,mahori/brew,ilovezfs/brew,pseudocody/brew,reitermarkus/brew,claui/brew,Linuxbrew/brew,sjackman/homebrew,maxim-belkin/brew,pseudocody/brew,DomT4/brew,konqui/brew,MikeMcQuaid/brew,reelsense/brew,EricFromCanada/brew,reitermarkus/brew,DomT4/brew,reelsense/brew,Homebrew/brew,Linuxbrew/brew,claui/brew