Make tools/submit_try safer

tools/submit_try

Index: tools/submit_try
diff --git a/tools/submit_try b/tools/submit_try
index e371afb23a05975ee5a74b92bfb2e1cf1e65f4e4..6647b89e1c1a8593de73314bbe958d156ffb87da 100755
--- a/tools/submit_try
+++ b/tools/submit_try
@@ -286,15 +286,17 @@ def SubmitTryRequest(args, is_svn=True):
     cmd = [GIT, 'diff', git_cl.Changelist().GetUpstreamBranch(),
            '--no-ext-diff']
     proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    if proc.wait() != 0:
+    git_data = proc.communicate()
+    if git_data[0] is None:
       raise Exception('Failed to capture git diff!')
 
     temp_dir = tempfile.mkdtemp()
     try:
       diff_file = os.path.join(temp_dir, 'patch.diff')
       with open(diff_file, 'wb') as f:
-        f.write(proc.communicate()[0])
-  
+        f.write(git_data[0])
+        f.close()
+
       try_args = ['--use_svn',
                   '--svn_repo', GetTryRepo(),
                   '--root', GetCheckoutRoot(is_svn),