channeled_transport: check socket before write

Fix a backtrace got on play store vitals

Change-Id: Id8333476073ab5aca253a9e69a48bf364018d0fc

src/jamidht/channeled_transport.cpp

@@ -292,14 +292,14 @@ 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()) {
-        std::error_code ec;
-        socket_->write(reinterpret_cast<const uint8_t*>(tdata->buf.start), size, ec);
-        lk.unlock();
-        if (ec) {
-            return PJ_EINVAL;
+    if (txQueue_.empty()) {
+        if (socket_) {
+            std::error_code ec;
+            socket_->write(reinterpret_cast<const uint8_t*>(tdata->buf.start), size, ec);
+            if (!ec)
+                return PJ_SUCCESS;
         }
-        return PJ_SUCCESS;
+        return PJ_EINVAL;
     }
 
     // Asynchronous sending