Network Remote: Check bytesAvailable >= 4 before reading length integer

This caused Clementine Remote to stop working on Android N. writeInt()
splits the 4 bytes across multiple tcp frames. Clementine would read
a wrong length and thus fail to read any protocol buffer data.

src/networkremote/remoteclient.cpp

@@ -64,6 +64,10 @@ void RemoteClient::setDownloader(bool downloader) { downloader_ = downloader; }
 void RemoteClient::IncomingData() {
   while (client_->bytesAvailable()) {
     if (!reading_protobuf_) {
+      // If we have less than 4 byte, we cannot read the length. Wait for more data
+      if (client_->bytesAvailable() < 4) {
+        break;
+      }
       // Read the length of the next message
       QDataStream s(client_);
       s >> expected_length_;