Fix default cwd value and the timing of the result code check

gclient_scm.py

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Gclient-specific SCM-specific operations."""
 
 import logging
 import os
 import re
 import subprocess
@@ skipping 169 matching lines @@
       print('\n________ couldn\'t run status in %s:\nThe directory '
             'does not exist.' % self.checkout_path)
     else:
       merge_base = self._Run(['merge-base', 'HEAD', 'origin'])
       self._Run(['diff', '--name-status', merge_base], redirect_stdout=False)
       files = self._Run(['diff', '--name-only', merge_base]).split()
       file_list.extend([os.path.join(self.checkout_path, f) for f in files])
 
   def _Run(self, args, cwd=None, checkrc=True, redirect_stdout=True):
     # TODO(maruel): Merge with Capture?
+    if cwd is None:
+        cwd = self.checkout_path
     stdout=None
     if redirect_stdout:
       stdout=subprocess.PIPE
     if cwd == None:
       cwd = self.checkout_path
     cmd = [self.COMMAND]
     cmd.extend(args)
     sp = subprocess.Popen(cmd, cwd=cwd, stdout=stdout)
+    output = sp.communicate()[0]
     if checkrc and sp.returncode:
       raise gclient_utils.Error('git command %s returned %d' %
                                 (args[0], sp.returncode))
-    output = sp.communicate()[0]
     if output is not None:
       return output.strip()
 
 
 class SVNWrapper(SCMWrapper, scm.SVN):
   """ Wrapper for SVN """
 
   def cleanup(self, options, args, file_list):
     """Cleanup working copy."""
     __pychecker__ = 'unusednames=file_list,options'
@@ skipping 246 matching lines @@
           self.ReplaceAndPrint(line)
         else:
           if (line.startswith(self.original_prefix) or
               line.startswith(self.working_prefix)):
             self.ReplaceAndPrint(line)
           else:
             print line
 
     filterer = DiffFilterer(self.relpath)
     self.RunAndFilterOutput(command, path, False, False, filterer.Filter)