More robust check that VIRUAL_ENV is valid

Author: oleksandr-pavlyk

dpctl/_init_helper.py

@@ -22,6 +22,8 @@
     # with DPC++ libraries to the DLL search path gh-1745
     if "VIRTUAL_ENV" in os.environ:
         venv_dir = os.environ["VIRTUAL_ENV"]
-        expected_dir = os.path.join(venv_dir, "Library", "bin")
-        if os.path.exists(expected_dir):
-            os.add_dll_directory(expected_dir)
+        # Expect to find file per PEP-0405
+        expected_file = os.path.join(venv_dir, "pyvenv.cfg")
+        dll_dir = os.path.join(venv_dir, "Library", "bin")
+        if os.path.isdir(dll_dir) and os.path.isfile(expected_file):
+            os.add_dll_directory(dll_dir)