[PATCH] py3: use str to query registry values on Windows

[Matt Harbison]

# HG changeset patch
# User Matt Harbison <matt_harbison at yahoo.com>
# Date 1539380085 14400
#      Fri Oct 12 17:34:45 2018 -0400
# Node ID 473751b3bbfce976fd6a821859d1d45f27c1ace1
# Parent  5b8bab9a7e07692e8d827c5315502301a11e4803
py3: use str to query registry values on Windows

This blew up launching any command if extdiff processed a tool with a regkey
config.

diff --git a/mercurial/windows.py b/mercurial/windows.py
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -583,7 +583,8 @@ def lookupreg(key, valname=None, scope=N
     for s in scope:
         try:
             with winreg.OpenKey(s, encoding.strfromlocal(key)) as hkey:
-                val = winreg.QueryValueEx(hkey, valname)[0]
+                val = winreg.QueryValueEx(hkey,
+                                          encoding.strfromlocal(valname))[0]
                 # never let a Unicode string escape into the wild
                 return encoding.unitolocal(val)
         except EnvironmentError: