bpo-39897: Remove needless Path(self.parent) call, which makes is_mount() misbehave in Path subclasses. (GH-18839)

Author: barneygale

Lib/pathlib.py

@@ -1438,17 +1438,16 @@ def is_mount(self):
         if not self.exists() or not self.is_dir():
             return False
 
-        parent = Path(self.parent)
         try:
-            parent_dev = parent.stat().st_dev
+            parent_dev = self.parent.stat().st_dev
         except OSError:
             return False
 
         dev = self.stat().st_dev
         if dev != parent_dev:
             return True
         ino = self.stat().st_ino
-        parent_ino = parent.stat().st_ino
+        parent_ino = self.parent.stat().st_ino
         return ino == parent_ino
 
     def is_symlink(self):