Revert backend path changes

Author: roaffix

arrayfire_wrapper/_backend.py

@@ -49,11 +49,18 @@ def _get_backend_path_config() -> _BackendPathConfig:
     platform_name = platform.system()
     cuda_found = False
 
-    # Try to use user provided AF_PATH if explicitly set
-    af_path = os.environ.get("AF_PATH", None)
-    af_is_user_path = af_path is not None
+    # try to use user provided AF_PATH if explicitly set
+    try:
+        af_path = Path(os.environ["AF_PATH"])
+        af_is_user_path = True
+    except KeyError:
+        af_path = None
+        af_is_user_path = False
 
-    cuda_path = os.environ.get("CUDA_PATH", None)
+    try:
+        cuda_path = Path(os.environ["CUDA_PATH"])
+    except KeyError:
+        cuda_path = None
 
     # Try to find default arrayfire installation paths
     if platform_name == _SupportedPlatforms.windows.value or _SupportedPlatforms.is_cygwin(platform_name):