Powerspectrum triggers assertion

[t-b]

Open a file in the analysis browser, open a sweepbrowser and execute the following SF code:

trange = [0, inf]
sel = select(selrange($trange),selchannels(AD), selsweeps())
dat = data($sel)

powerspectrum($dat, default, avg)

triggers

  !!! Assertion FAILED !!!
  Message: "Can not work with NaN as mapIndex"
  Please provide the following information if you contact the MIES developers:
  ################################
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Stacktrace:
  SF_button_sweepFormula_display(...)#L3016 [MIES_SweepFormula.ipf]
SF_FormulaPlotter(...)#L1955 [MIES_SweepFormula.ipf]
SF_GetTraceColor(...)#L1521 [MIES_SweepFormula.ipf]
SFH_GetLabNoteBookForSweep(...)#L1937 [MIES_SweepFormula_Helpers.ipf]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Time: 2025-04-09T13:52:24+02:00
  Locked device: [- none -]
  Current sweep: [- none -]
  DAQ: [- none -]
  Testpulse: [- none -]
  Acquisition state: [- none -]
  Experiment: Untitled ()
  Igor Pro version: 9.0.6.1 (56704)
  MIES version:
  Release_2.8_20240925-356-g193bf8076
Date and time of last commit: 2025-04-08T21:46:42+02:00
Submodule status: 
-f7e1cfa52796165f589ab628174a0c4307459b92 Packages/IPNWB
-7dece9a54731855b702ee6002650af72e8a3daa4 Packages/doc/doxygen-filter-ipf
-b6543f4e52ec0dab137cbe7405e9500bb29a0caf Packages/igortest
  ################################

The reason is that the average trace does not have SF_META_SWEEPMAPINDEX JWN data. But maybe we should special average traces in SF_GetTraceColor and give them their pink as usual or color groups support.