[ChromeDriver] Fix a bug in client_replay.py

Checking if log parser returns an empty value then
we should return 'command'

Change-Id: Ia6f2b583603f04183349a023365e13aceff95894
Reviewed-on: https://chromium-review.googlesource.com/c/1331950Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Artur Khachatryan <khachatryan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613154}

chrome/test/chromedriver/log_replay/client_replay.py

@@ -731,6 +731,8 @@ class CommandSequence(object):
         self._id_map, self._binary, self._base_url)
 
     response = self._parser.GetNext()
+    if not response:
+      return command
     if not response.IsResponse():
       raise ReplayException("Command and Response unexpectedly out of order.")
     self._IngestLoggedResponse(response)