Fix logic for checking whether git is installed.

bootstrap/win/win_tools.bat

 @echo off
 :: Copyright (c) 2012 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.
 
 :: This script will try to find if svn and python are accessible and it not,
 :: it will try to download it and 'install' it in depot_tools.
 
 :: Sadly, we can't use SETLOCAL here otherwise it ERRORLEVEL is not correctly
 :: returned.
 
 set WIN_TOOLS_ROOT_URL=http://src.chromium.org/svn/trunk/tools
 set GIT_BIN_DIR=git-1.8.0_bin
 
 :: Get absolute root directory (.js scripts don't handle relative paths well).
 pushd %~dp0..\..
 set WIN_TOOLS_ROOT_DIR=%CD%
 popd
 
 if "%1" == "force" (
   set WIN_TOOLS_FORCE=1
   shift /1
 )
 
 
 :GIT_CHECK
 :: If the batch file exists, skip the git check.
-if not exist "%WIN_TOOLS_ROOT_DIR%\%GIT_BIN_DIR%" goto :GIT_INSTALL
+if exist "%WIN_TOOLS_ROOT_DIR%\%GIT_BIN_DIR%" goto :SVN_CHECK
 if "%CHROME_HEADLESS%" == "1" goto :SVN_CHECK
 if "%WIN_TOOLS_FORCE%" == "1" goto :GIT_INSTALL
 call git --version 2>nul 1>nul
 if errorlevel 1 goto :GIT_INSTALL
 goto :SVN_CHECK
 
 
 :GIT_INSTALL
 echo Installing git (avg 1-2 min download) ...
 :: git is not accessible; check it out and create 'proxy' files.
@@ skipping 100 matching lines @@
 goto :END
 
 
 :returncode
 set WIN_TOOLS_ROOT_URL=
 set WIN_TOOLS_ROOT_DIR=
 exit /b %ERRORLEVEL%
 
 :END
 call :returncode %ERRORLEVEL%