Use reasonable defaults or require user interactions

[mlt]

If user accesses certain menu action from non-standard entry point, certain QGis settings may not be initialized.

@AlisterH reports

Enable the plugin, click to start the Time Series Plots or Spatial Plots module, select a simulation output which has already been calculated (e.g. from the sample data), and click "New Plot". QGIS will crash. If you use a debugger you will see that it is caused by a division by zero error in
TIME_STEP = TIME_STEP / p->readNumEntry("pihm", var.arg(index[variableIndex]));
or
int steps = p->readNumEntry("pihm", var.arg(index[comboBoxEleVariable->currentIndex()]));

It happens because scales are not set (or loaded via QgsProject).