add_powder_histogram does not accept instrument parameters as dicts

[ezatterin]

Consider the following example:

import GSASII as gs
from GSASII import GSASIIscriptable as gsc

# initialise new project
gpx = gsc.G2Project(newgpx="test.gpx")

# load powder diffraction readers
readers = gs.GSASIIfiles.LoadImportRoutines("pwd")

# specify instrmental parameters dictionaries
inst_params = [
    {
        "Type": ["PXC", "PXC", 0],
        "Lam": [1.5405, 1.5405, 0],
        "Zero": [0.0, 0.0, 0],
        "Polariz.": [0.7, 0.7, 0],
        "U": [2.0, 2.0, 0],
        "V": [-2.0, -2.0, 0],
        "W": [5.0, 5.0, 0],
        "X": [0.0, 0.0, 0],
        "Y": [0.0, 0.0, 0],
        "Z": [0.0, 0.0, 0],
        "SH/L": [0.002, 0.002, 0],
        "Azimuth": [0.0, 0.0, 0],
        "Bank": [1, 1, 0],
    },
    {},
]

# load the powder histogram
hist = gpx.add_powder_histogram(datafile="some_data_file.xye", iparams=inst_params)

the last line fails with:

File ~/venvs/py3.12/lib/python3.12/site-packages/GSASII/GSASIIscriptable.py:1068, in G2Project.add_powder_histogram(self, datafile, iparams, phases, fmthint, databank, instbank, multiple, URL)
   1066         pass
   1067 for r in pwdrreaders:
-> 1068     histname, new_names, pwdrdata = load_pwd_from_reader(r, iparmfile,
   1069                                   [h.name for h in self.histograms()],bank=instbank)
   1070     if histname in self.data:
   1071         G2fil.G2Print("Warning - redefining histogram", histname)

UnboundLocalError: cannot access local variable 'iparmfile' where it is not associated with a value

This is because the variable iparmfile is never set unless the iparams keyword argument of GSASIIscriptable.G2Project.add_powder_histogram is equal to a string pointing to a file, see lines 1062-1066:

  if URL:
      iparmfile = downloadFile(iparams)
  else:
      try:
          iparmfile = os.path.abspath(os.path.expanduser(iparams))
      except:
          pass

this is despite it is stated in the docstring of the function that

:param str iparams: A filename for an instrument parameters file,
            or a pair of instrument parameter dicts from :func:`load_iprms`.
            This may be omitted for readers that provide the instrument
            parameters in the file. (Only a few importers do this.)

I will make a PR soon.