Check for clang-format only if its files are present

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index b6d32d15a6a6c0448b6a7210e962c794b4de59c9..0c770cb58cf6b3127937cc53c87903006af04412 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -4440,17 +4440,17 @@ 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: