Fix manpath detection
Fix manpath detection

Checking for MANPATH without quotes always returns true, so that it breaks bash-completion for man pages on modern systems without MANPATH environment variable.
shlevy/nix,rycee/nix,pikajude/nix,dezgeg/nix,dezgeg/nix,NixOS/nix,shlevy/nix,peti/nix,pikajude/nix,NixOS/nix,dtzWill/nix,layus/nix,layus/nix,zimbatm/nix,dtzWill/nix,ehmry/nix,layus/nix,shlevy/nix,ehmry/nix,dezgeg/nix,peti/nix,ehmry/nix,zimbatm/nix,rycee/nix,peti/nix,ehmry/nix,shlevy/nix,vcunat/nix,NixOS/nix,NixOS/nix,rycee/nix,ehmry/nix,dezgeg/nix,rycee/nix,zimbatm/nix,pikajude/nix,vcunat/nix,ehmry/nix,peti/nix,NixOS/nix,dtzWill/nix,zimbatm/nix,layus/nix,dezgeg/nix,vcunat/nix,shlevy/nix,peti/nix,vcunat/nix,dtzWill/nix,layus/nix,rycee/nix,dtzWill/nix