refactor: simplify registry reads with setuphelpers

setup.py

@@ -63,10 +63,11 @@ def _read_value(path, name):
     subkey = _registry_path(path)
     if not reg_key_exists(HKEY_LOCAL_MACHINE, subkey):
         return {'Exists': False, 'Value': None}
-    if not reg_value_exists(HKEY_LOCAL_MACHINE, subkey, name):
+    missing = object()
-        return {'Exists': False, 'Value': None}
     with reg_openkey_noredir(HKEY_LOCAL_MACHINE, subkey) as key:
-        value = reg_getvalue(key, name)
+        value = reg_getvalue(key, name, default=missing)
+    if value is missing:
+        return {'Exists': False, 'Value': None}
     if value is None:
         raise RuntimeError('Registry value disappeared while it was being read: %s' % name)
     try: