Check for clang-format only if its files are present

R=agable@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1880013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299867 0039d316-1c4b-4281-b951-d872f2087c98

git_cl.py

@@ -4461,17 +4461,17 @@ def CMDformat(parser, args):
   top_dir = os.path.normpath(
       RunGit(["rev-parse", "--show-toplevel"]).rstrip('\n'))
 
-  # Locate the clang-format binary in the checkout
-  try:
-    clang_format_tool = clang_format.FindClangFormatToolInChromiumTree()
-  except clang_format.NotFoundError, e:
-    DieWithError(e)
-
   # Set to 2 to signal to CheckPatchFormatted() that this patch isn't
   # formatted. This is used to block during the presubmit.
   return_value = 0
 
   if clang_diff_files:
+    # Locate the clang-format binary in the checkout
+    try:
+      clang_format_tool = clang_format.FindClangFormatToolInChromiumTree()
+    except clang_format.NotFoundError, e:
+      DieWithError(e)
+
     if opts.full:
       cmd = [clang_format_tool]
       if not opts.dry_run and not opts.diff: