Set variables to avoid false-positive compiler warnings.

../tool/transport_common.cc:429:14: error: ‘code_250’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

(I don't believe it can actually happen though.)

Change-Id: I78d19ad42ed4c05404f1d8d3e8f254ede3244b8d

tool/transport_common.cc

diff --git a/tool/transport_common.cc b/tool/transport_common.cc
index 735a349..01bba00 100644
--- a/tool/transport_common.cc
+++ b/tool/transport_common.cc
@@ -483,7 +483,7 @@
 bool DoSMTPStartTLS(int sock) {
   SocketLineReader line_reader(sock);
 
-  unsigned code_220;
+  unsigned code_220 = 0;
   std::string reply_220;
   if (!line_reader.ReadSMTPReply(&code_220, &reply_220)) {
     return false;
@@ -500,7 +500,7 @@
     return false;
   }
 
-  unsigned code_250;
+  unsigned code_250 = 0;
   std::string reply_250;
   if (!line_reader.ReadSMTPReply(&code_250, &reply_250)) {
     return false;