[PATCH 2/2] BaseTools: explicitly import email.header PatchCheck.py

["Leif Lindholm" <leif@nuviainc.com>]

On Debian 10 (Buster), when running PatchCheck.py with python2, a
backtrace is printed, starting from:

  File "../edk2/BaseTools/Scripts/PatchCheck.py", line 595,
   in find_patch_pieces
    parts = email.header.decode_header(pmail.get('subject'))
  AttributeError: 'module' object has no attribute 'header'

When using python3, this backtrace does not appear.

Explicitly importing email.header resolves this for python2 and does not
appear to cause any issues with python3.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
---
 BaseTools/Scripts/PatchCheck.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/BaseTools/Scripts/PatchCheck.py b/BaseTools/Scripts/PatchCheck.py
index 527761986d4c..52244b0bc4d8 100755
--- a/BaseTools/Scripts/PatchCheck.py
+++ b/BaseTools/Scripts/PatchCheck.py
@@ -20,6 +20,8 @@ import re
 import subprocess
 import sys
 
+import email.header
+
 class Verbose:
     SILENT, ONELINE, NORMAL = range(3)
     level = NORMAL
-- 
2.20.1