After running a simulation and auto scale x axis is checked, if you change the time end to a different value, the plot scales the x axis to the new end time but does not clear out the old plot.

[bartjuw]

Reproduce:

1. With default model loaded, check the 'Autocale X' box.
2. Run simulate
3. Change 'Time end' from 20 to 30.
   Result:
   In the plot page the x-axis (time) scaled from 0 to 20 goes to 0 to 30 but the actual data points of the curves do not change.

Expected: When 'Autoscale X' is checked: if you change the 'Time end' value it is not reflected in the plot until the next simulation is run.