small bugfix in retri setup without spectra

for cases where there is dense photometry but not spectroscopy, one may still want to run a retrieval. the bugfix patches an instance where a breaking error would be thrown by setup_retrieval when inc_spec=False

species/fit/retrieval.py

@@ -3583,7 +3583,8 @@ def setup_retrieval(
 
         for spec_value in self.spectrum.values():
             data_spec_res.append(spec_value[3])
-
+        if len(data_spec_res) == 0:
+            data_spec_res.append(40) # for photometry only retrievals
         max_spec_res = max(data_spec_res)
 
         if max_spec_res > 1000.0 and self.res_mode == "c-k":