Zooming on y should still be supported when autoranging on y

[jbednar]

Auto-ranging on y when zooming was added in #5554, which is great, but based on the behavior in #5621 (comment), it appears to be overriding an explicit zoom event on y, which I don't think is correct.

I haven't tried the code myself, but what it appears to do is to auto-range on y after any zoom event, while I think it should only auto-range on y after an x (or both x and y) zoom event. If someone explicitly zooms on y alone, I think that should be respected, not eliminated. Auto-ranging should be helpful, not prohibitive!