Add/clean up some CHECKs in LogReader.

Specifically:
 - If we reach a point where we have a multi-node config but
   none of the nodes have logs to replay, immediately crash.
 - Correctly compare the logged_configuration to the replay
   configuration for checking node list length, rather than
   comparing the replay configuration to itself.

Change-Id: Ibd2da62cacab45153361cafb746102c42711f0d5
diff --git a/aos/events/logging/logger.cc b/aos/events/logging/logger.cc
index de9d344..b3472d7 100644
--- a/aos/events/logging/logger.cc
+++ b/aos/events/logging/logger.cc
@@ -312,9 +312,16 @@
     state->channel_merger = std::make_unique<ChannelMerger>(filenames);
   } else {
     if (replay_configuration) {
-      CHECK_EQ(configuration()->nodes()->size(),
+      CHECK_EQ(logged_configuration()->nodes()->size(),
                replay_configuration->nodes()->size())
           << ": Log file and replay config need to have matching nodes lists.";
+      for (const Node *node : *logged_configuration()->nodes()) {
+        if (configuration::GetNode(replay_configuration, node) == nullptr) {
+          LOG(FATAL)
+              << "Found node " << FlatbufferToJson(node)
+              << " in logged config that is not present in the replay config.";
+        }
+      }
     }
     states_.resize(configuration()->nodes()->size());
   }
@@ -387,6 +394,11 @@
 
     Register(state->event_loop_unique_ptr.get());
   }
+  if (live_nodes_ == 0) {
+    LOG(FATAL)
+        << "Don't have logs from any of the nodes in the replay config--are "
+           "you sure that the replay config matches the original config?";
+  }
 
   // We need to now seed our per-node time offsets and get everything set up to
   // run.