cmd/upgrade: handle nil runtime_dependencies.
cmd/upgrade: handle nil runtime_dependencies.

Fixes #7360

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