channeled_transport: check socket before write

Fix a backtrace got on play store vitals

Change-Id: Id8333476073ab5aca253a9e69a48bf364018d0fc

src/jamidht/channeled_transport.cpp

@@ -292,15 +292,15 @@ ChanneledSIPTransport::send(pjsip_tx_data* tdata,
     // Check in we are able to send it in synchronous way first
     const std::size_t size = tdata->buf.cur - tdata->buf.start;
     std::unique_lock<std::mutex> lk {txMutex_};
-    if (/*TODO handle disconned: syncTx_ and*/ txQueue_.empty()) {
+    if (txQueue_.empty()) {
+        if (socket_) {
             std::error_code ec;
             socket_->write(reinterpret_cast<const uint8_t*>(tdata->buf.start), size, ec);
-        lk.unlock();
-        if (ec) {
-            return PJ_EINVAL;
-        }
+            if (!ec)
                 return PJ_SUCCESS;
         }
+        return PJ_EINVAL;
+    }
 
     // Asynchronous sending
     tdata->op_key.tdata = tdata;