We still want to "write" empty messages

So that the size of the messages queue can go to zero

src/connection.cpp

@@ -69,17 +69,13 @@ bool Connection::writeBytes() {
     for (auto it = messages_.begin();
          it != messages_.end() && iov_count < IOV_MAX; ++it) {
       const auto &msg = *it;
-      if (msg.size() > 0) {
       iov[iov_count] = {
           const_cast<void *>(static_cast<const void *>(msg.data())),
           msg.size()};
       iov_count++;
     }
-    }
 
-    if (iov_count == 0) {
-      break;
-    }
+    assert(iov_count > 0);
 
     ssize_t w;
     for (;;) {