Fix a log-reading bug

I can't manage to reproduce it in a test, but the new CHECK should catch
it robustly.

Change-Id: I4e8baab929326bd3de12865d37703796d5cf2417
diff --git a/aos/events/logging/logger.cc b/aos/events/logging/logger.cc
index e767427..8969ee2 100644
--- a/aos/events/logging/logger.cc
+++ b/aos/events/logging/logger.cc
@@ -599,7 +599,9 @@
   // to timestamps on log files where the timestamp log file starts before the
   // data.  In this case, it is reasonable to expect missing data.
   ignore_missing_data_ = true;
+  VLOG(1) << "Running until start time: " << start_time;
   event_loop_factory_->RunFor(start_time.time_since_epoch());
+  VLOG(1) << "At start time";
   // Now that we are running for real, missing data means that the log file is
   // corrupted or went wrong.
   ignore_missing_data_ = false;