Fix STARTTLS detection.

The previous code was not an impressive demonstration of clear thinking
and could reject cases where STARTTLS was actually supported.

Change-Id: I27ce8b401447a49be93f58c9e4eb5c5d8e7b73d4
Reviewed-on: https://boringssl-review.googlesource.com/10241
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

tool/transport_common.cc

diff --git a/tool/transport_common.cc b/tool/transport_common.cc
index ed1bc0f..23fa3bb 100644
--- a/tool/transport_common.cc
+++ b/tool/transport_common.cc
@@ -535,8 +535,7 @@
   }
 
   // https://tools.ietf.org/html/rfc1869#section-4.3
-  if (reply_250.find("\nSTARTTLS\n") == std::string::npos &&
-      reply_250.find("\nSTARTTLS") != reply_250.size() - 8) {
+  if (("\n" + reply_250 + "\n").find("\nSTARTTLS\n") == std::string::npos) {
     fprintf(stderr, "Server does not support STARTTLS\n");
     return false;
   }