obsexchange: make compatible with some unreleased 4.5 versions We don't generally care to be compatible with unreleased versions of hg, but this is just a one-line change to be compatible with a range of commits before 158d4ecc03c8 (wireprotoserver: move all wire protocol handling logic out of hgweb, 2018-03-08), so hopefull it can be worth it.