Bugfixes for python agents obstacle detection when empty vehicle_list is passed. (#7142)

* Bugfix for empty vehicle_list

Bug description: When an empty list is passed this fills the list with all vehicles; this is not intended. 

1) This does not allow to pass an empty list, e.g. if no vehicles are nearby.

2) On a map without pedestrians, this code is also used with an empty list which then detects cars as pedestrians.

* Update CHANGELOG.md with agent bugfix note

---------

Co-authored-by: Blyron <53337103+Blyron@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,7 @@
  * Added functions to get actor' bones and components names
  * Added functions to get actor' sockets transforms
  * make PythonAPI Windows: Fixed incompatibility issue with Anaconda due `py` command.
+ * Fixed bug in python agents when vehicle list was empty causing a check on all vehicles (BasicAgent.py) and detected pedestrians as vehicles if no pedestrains are present (BehaviourAgent.py) 
 
 ## CARLA 0.9.15
 

PythonAPI/carla/agents/navigation/basic_agent.py

@@ -345,12 +345,14 @@ class BasicAgent(object):
                 return None
 
             return Polygon(route_bb)
-
+      
         if self._ignore_vehicles:
             return (False, None, -1)
 
-        if not vehicle_list:
+        if vehicle_list is None:
             vehicle_list = self._world.get_actors().filter("*vehicle*")
+        if len(vehicle_list) == 0:
+            return (False, None, -1)
 
         if not max_distance:
             max_distance = self._base_vehicle_threshold