Fixup for 62843e88 - max(x,x) is a really stupid bug here
Fix: We don't need a `cmp` variable here

The case that the `cmp` variable is excluded, as this would mean that
the node is already in the tree, whereas this function is assumed NOT to
be called in this case.

So we don't need to check for `cmp == 0`. Because this leaves us two
possible cases, we can simply remove the `cmp` variable and embedd the
hash comparison right into the if condition.