Fix: GPX export fails on huge tracks, closes #54

import org.xmlpull.v1.XmlSerializer;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.StringWriter;

import java.io.OutputStreamWriter;

import java.nio.charset.Charset;

import androidx.annotation.NonNull;

import androidx.core.app.ActivityCompat;

            file = getFile(dir, trackName + "_" + (++i));

        }

        try (FileOutputStream fileOutputStream = new FileOutputStream(file)) {

        try (FileOutputStream stream = new FileOutputStream(file);

             OutputStreamWriter writer = new OutputStreamWriter(stream, Charset.forName("UTF-8"));

             BufferedWriter bufferedWriter = new BufferedWriter(writer)) {

            XmlSerializer serializer = Xml.newSerializer();

            StringWriter writer = new StringWriter();

            serializer.setOutput(writer);

            serializer.setOutput(bufferedWriter);

            // header

            serializer.startDocument("UTF-8", true);

            serializer.endDocument();

            serializer.flush();

            String dataWrite = writer.toString();

            fileOutputStream.write(dataWrite.getBytes());

            fileOutputStream.flush();

            if (Logger.DEBUG) { Log.d(TAG, "[export gpx file written to " + file.getPath()); }

            sendBroadcast(BROADCAST_EXPORT_DONE, null);

        } catch (IOException|IllegalArgumentException|IllegalStateException e) {