fix the crash when the path to psf/fd data is not given

ObservationSim/Config/Config.py

@@ -21,8 +21,10 @@ def config_dir(config, work_dir=None, data_dir=None):
     # Object catalog direcotry
     path_dict["cat_dir"] = os.path.join(path_dict["data_dir"], config["input_path"]["cat_dir"])
     # PSF data directory
-    path_dict["psf_dir"] = os.path.join(path_dict["data_dir"], config["psf_setting"]["psf_dir"])
-    path_dict["fd_path"] = os.path.join(path_dict["data_dir"], config["psf_setting"]["fd_path"])
+    if config["psf_setting"]["psf_model"] == "Interp":
+        path_dict["psf_dir"] = os.path.join(path_dict["data_dir"], config["psf_setting"]["psf_dir"])
+    if config["ins_effects"]["field_dist"] == True:
+        path_dict["fd_path"] = os.path.join(path_dict["data_dir"], config["psf_setting"]["fd_path"])
 
     return path_dict