D'oh. That's what I get for not paying attention and looking at the indentation instead of for braces. Still, my bet's on mismerge first - though it'd be worth reviewing that committer's other changes.
++ on mismerge. The change likely won't impact the output binary - compiler should issue a warning, which devs might ignore; then the optimizer would remove it as unreachable.
Perhaps the developer deliberately allowed that mismerge to give himself an aura of incompetence/sloppiness, enhancing his plausible deniability when it is discovered that one of his other changes led to an insidious vulnerability. But more likely it was just an accident - if he were malicious, the effect of bringing attention to his code would be highly undesirable.