metrics: 'Send' method crashes on NULL ErrorPtr

TEST=manually tested on panther_embedded
BUG=none

Change-Id: Iced380180918839d34a46e1cb2743a4cffdd5b4c
Reviewed-on: https://chromium-review.googlesource.com/220780
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Nathan Bullock <nathanbullock@google.com>
Tested-by: Nathan Bullock <nathanbullock@google.com>
diff --git a/metrics/uploader/sender_http.cc b/metrics/uploader/sender_http.cc
index 585287f..7b5228a 100644
--- a/metrics/uploader/sender_http.cc
+++ b/metrics/uploader/sender_http.cc
@@ -29,7 +29,9 @@
       chromeos::http::Transport::CreateDefault(),
       &error);
   if (!response || response->GetDataAsString() != "OK") {
-    DLOG(ERROR) << "Failed to send data: " << error->GetMessage();
+    if (error) {
+      DLOG(ERROR) << "Failed to send data: " << error->GetMessage();
+    }
     return false;
   }
   return true;