Avoid adding PathEntryFinder if not necessary

Author: abravalheri

setuptools/command/editable_wheel.py

@@ -563,6 +563,10 @@ def find_module(cls, fullname):
 def install():
     if not any(finder == _EditableFinder for finder in sys.meta_path):
         sys.meta_path.append(_EditableFinder)
+
+    if not NAMESPACES:
+        return
+
     if not any(hook == _EditableNamespaceFinder._path_hook for hook in sys.path_hooks):
         # PathEntryFinder is needed to create NamespaceSpec without private APIS
         sys.path_hooks.append(_EditableNamespaceFinder._path_hook)