doctor: don't complain if reads_brewed_pth_files? is nil
doctor: don't complain if reads_brewed_pth_files? is nil

Closes Homebrew/homebrew#33957.

vitorgalvao/brew,EricFromCanada/brew,nandub/brew,DomT4/brew,reitermarkus/brew,reitermarkus/brew,palxex/brew,muellermartin/dist,JCount/brew,pseudocody/brew,vitorgalvao/brew,vitorgalvao/brew,AnastasiaSulyagina/brew,palxex/brew,DomT4/brew,pseudocody/brew,jmsundar/brew,Homebrew/brew,Linuxbrew/brew,mgrimes/brew,Linuxbrew/brew,aw1621107/brew,maxim-belkin/brew,MikeMcQuaid/brew,gregory-nisbet/brew,rwhogg/brew,konqui/brew,gregory-nisbet/brew,reelsense/brew,claui/brew,maxim-belkin/brew,Linuxbrew/brew,amar-laksh/brew_sudo,aw1621107/brew,gordonmcshane/homebrew,sjackman/homebrew,AnastasiaSulyagina/brew,toonetown/homebrew,hanxue/linuxbrew,konqui/brew,alyssais/brew,palxex/brew,mahori/brew,zmwangx/brew,reelsense/brew,toonetown/homebrew,mahori/brew,JCount/brew,amar-laksh/brew_sudo,alyssais/brew,konqui/brew,EricFromCanada/brew,bfontaine/brew,sjackman/homebrew,tonyg/homebrew,jmsundar/brew,JCount/brew,rwhogg/brew,reitermarkus/brew,claui/brew,reitermarkus/brew,AnastasiaSulyagina/brew,gregory-nisbet/brew,pseudocody/brew,konqui/brew,nandub/brew,MikeMcQuaid/brew,hanxue/linuxbrew,JCount/brew,staticfloat/brew,gordonmcshane/homebrew,ilovezfs/brew,mistydemeo/homebrew,ilovezfs/brew,aw1621107/brew,jmsundar/brew,hanxue/linuxbrew,ilovezfs/brew,muellermartin/dist,gordonmcshane/homebrew,EricFromCanada/brew,DomT4/brew,rwhogg/brew,tonyg/homebrew,reelsense/brew,MikeMcQuaid/brew,nandub/brew,mgrimes/brew,claui/brew,EricFromCanada/brew,staticfloat/brew,maxim-belkin/brew,sjackman/homebrew,mahori/brew,DomT4/brew,zmwangx/brew,claui/brew,mahori/brew,bfontaine/brew,zmwangx/brew,mgrimes/brew,tonyg/homebrew,vitorgalvao/brew,Linuxbrew/brew,alyssais/brew,Homebrew/brew,bfontaine/brew,Homebrew/brew,MikeMcQuaid/brew,amar-laksh/brew_sudo,muellermartin/dist,mistydemeo/homebrew,toonetown/homebrew,mistydemeo/homebrew,staticfloat/brew,nandub/brew,Homebrew/brew,sjackman/homebrew