buffet: support using default flag values

A previous change added support for overridding the configuration and
state paths, for testing, but resulted in the defaults not being used
since the empty string was passed for a flag value.  This changes the
init script so that empty paths from the upstart environment are not
used as flag values.

TEST=built, tested on device, tested with override
BUG=none

Change-Id: Id680ec7434b4c523cd0a2c8419dcf342a0a34199
Reviewed-on: https://chromium-review.googlesource.com/248580
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Aaron Kemp <kemp@google.com>
Tested-by: Aaron Kemp <kemp@google.com>

buffet/main.cc

diff --git a/buffet/main.cc b/buffet/main.cc
index 1dc3388..ab3798a 100644
--- a/buffet/main.cc
+++ b/buffet/main.cc
@@ -60,11 +60,13 @@
                 "Path to file containing config information.");
   DEFINE_string(state_path, kDefaultStateFilePath,
                 "Path to file containing state information.");
+  chromeos::FlagHelper::Init(argc, argv, "Privet protocol handler daemon");
+
   if (FLAGS_config_path.empty())
     FLAGS_config_path = kDefaultConfigFilePath;
   if (FLAGS_state_path.empty())
     FLAGS_state_path = kDefaultStateFilePath;
-  chromeos::FlagHelper::Init(argc, argv, "Privet protocol handler daemon");
+
   chromeos::InitLog(chromeos::kLogToSyslog | chromeos::kLogHeader);
   buffet::Daemon daemon{base::FilePath{FLAGS_config_path},
                         base::FilePath{FLAGS_state_path}};