Useless if-cond should not trigger useless-var messaging

[mduvall]

The code below returns W: Useless assignment to variable - foo.. This is not so much a useless assignment as a useless condition (since both branches assign the variable to the same evaluated value).

def foo
  if bar
    foo = 1
  else
    foo = 1
  end

  foo.bar.baz
end

[alexdowad]

I'm opening a PR which fixes this.