Positional "constant" doesn't honor axis limits

[alshan]

# No limits - both labels are visible
p = (ggplot() +
    geom_label(aes(y=[10]), label="Data y=10") +
    geom_label(label="Const y=13", y = 13)
)
p

# y-axis is limited : "Const y=13" should not be visible.
p + ylim(10, 10)

This produces the same plot (shown above) even though label "Const y=13" is now beyond the scale limits.

[alshan]

completed in ac22aa7