Choosing too small Wavenumber Step crashes the program

[i-ilak]

Hi everyone,

after fetching some date in the line-by-line tab, I tried to plot in the Graphing tab. If you set the Graph Type to Transmitance Spectrum and then tick the Wavenumber Step (cm^{-1}), the program crashes with the error

[Err]  Wavenumber Step must be less than Instrumental Resolution
Traceback (most recent call last):
  File "/media/sf_vm_share/hapiest/src/widgets/graphing/graphing_widget.py", line 178, in graph
    self.graph_ts(standard_params)
  File "/media/sf_vm_share/hapiest/src/widgets/graphing/graphing_widget.py", line 287, in graph_ts
    self.data_name_error.setText(
AttributeError: 'NoneType' object has no attribute 'setText'
Aborted (core dumped)

While the first line, i.e. [Err] Wavenumber Step must be less than Instrumental Resolution, indicates that this error occured due to bad user input, crashing the program seems like bad handling of the exception.