Fix default scene arg being overwritten

- Repeat calls of gprMax.run() would reuse scene data from the last call

gprMax/config.py

@@ -279,7 +279,7 @@ class SimulationConfig:
 
         # Scenes parameter may not exist if user enters via CLI
         try:
-            self.scenes = args.scenes
+            self.scenes = args.scenes if args.scenes is not None else []
         except AttributeError:
             self.scenes = []
 

gprMax/gprMax.py

@@ -25,7 +25,7 @@ from .utilities.logging import logging_config
 
 # Arguments (used for API) and their default values (used for API and CLI)
 args_defaults = {
-    "scenes": [],
+    "scenes": None,
     "inputfile": None,
     "outputfile": None,
     "n": 1,