X-axis vanishes when difference between min and max is less than two

Hello,

When using QCharts there is an edge case which causes the X-axis to vanish which can come up when trying to use a QDateTimeAxis. If the minimum x-axis value has 13 digits or more, then the x-axis will disappear if the range of the x-axis is less than two. 

It is possible for this to come up when using a QDateTimeAxis as you need to use MSecsSinceEpoch resulting in vary large values on the x-axis. I have attached an example which shows the situation where the x-axis will disappear.