Fix realpath ValueError on null byte

Calling os.path.realpath with a path containg a null byte ("\x00")
it raised an ValueError on posix systems.

This fix will catch the ValueError similar to how other path operations are handling such an Error.
e.g. os.path.exists, os.path.ismount, os.fspath, os.path.islink

Lib/posixpath.py

@@ -460,7 +460,7 @@ def realpath(filename, *, strict=False):
             if not stat.S_ISLNK(st.st_mode):
                 path = newpath
                 continue
-        except OSError:
+        except (OSError, ValueError):
             if strict:
                 raise
             path = newpath

Lib/test/test_posixpath.py

@@ -646,6 +646,15 @@ def test_realpath_resolve_first(self):
             safe_rmdir(ABSTFN + "/k")
             safe_rmdir(ABSTFN)
 
+    @skip_if_ABSTFN_contains_backslash
+    def test_realpath_null_byte(self):
+        path_with_null_byte = ABSTFN + "/\x00"
+        try:
+            os.mkdir(ABSTFN)
+            self.assertEqual(realpath(path_with_null_byte), path_with_null_byte)
+        finally:
+            safe_rmdir(ABSTFN)
+
     def test_relpath(self):
         (real_getcwd, os.getcwd) = (os.getcwd, lambda: r"/home/user/bar")
         try: