Merge branch 'ua/call-repo-config-with-possibly-null-repository'

Since a call to repo_config() can be called with repo set to NULL these days, a command that is marked as RUN_SETUP in the builtin command table does not have to check repo with NULL before making the call. * ua/call-repo-config-with-possibly-null-repository: builtin/difftool: remove unnecessary if statement builtin/add: remove unnecessary if statement