The reasoning behind the original line may be lost to time as
it does not make much sense checking the position on the x-axis
to determine how to position the client on the y-axis.

In the context of multi-monitor setups the monitor y position
(m->my) may be greater than 0 (say 500), in which case the window
could be placed out of view if:
   - the window attributes have a 0 value for the y position and
   - we end up using the y position of bh (e.g. 22)

If the aim is to avoid a new floating client covering the bar then
restricting y position to be at least that of the window area
(m->wy) should cover the two cases of using a top bar and using a
bottom bar.