bpo-45582: Don't fail if ENV_PATH is None in getpath.py (GH-31699)

Author: tiran

Modules/getpath.py

@@ -277,7 +277,7 @@ def search_up(prefix, *landmarks, test=isfile):
     # executable path was provided in the config.
     real_executable = executable
 
-if not executable and program_name:
+if not executable and program_name and ENV_PATH:
     # Resolve names against PATH.
     # NOTE: The use_environment value is ignored for this lookup.
     # To properly isolate, launch Python with a full path.