[Charts] Alert line doesn't show if below data lowbound

In case the alert is set to a value lower than the data range (and use-zero-min-value is set to false), the alert line doesn't show.

Also if the alert was showing (due to being greater than the min value in the data) and is updated to a value lower than data range, it persists, incorrectly, at the previous position.

The correct behavior would be to update the Y scale to show the alert line.