dataset_analyzer: add option to force load flats

nabu/resources/dataset_analyzer.py

@@ -174,10 +174,10 @@ class HDF5DatasetAnalyzer(DatasetAnalyzer):
 
 
     def _get_flats_darks(self):
-        if len(self.flats) == 0:
+        if len(self.flats) == 0 and not(self.extra_options["force_flatfield"]):
             # No flats at all in the dataset. Do nothing.
             return
-        if self._load_flats_from_tomwer():
+        if self.processes_file is None and self._load_flats_from_tomwer():
             # Loaded from tomwer_processes.h5
             return
         # Otherwise load or compute flats/darks with nabu