Found a defect

[Mohamed Sabry]

Hi,

I tried merging an arabic srt with an english one and this happened :

class java.lang.NullPointerException:null
    io.github.bonigarcia.dualsub.srt.DualSrt.processDesync(DualSrt.java:254)
    io.github.bonigarcia.dualsub.srt.Merger.mergeSubs(Merger.java:99)
    io.github.bonigarcia.dualsub.srt.Worker.doInBackground(Worker.java:140)
    io.github.bonigarcia.dualsub.srt.Worker.doInBackground(Worker.java:38)
    javax.swing.SwingWorker$1.call(Unknown Source)
    java.util.concurrent.FutureTask.run(Unknown Source)
    javax.swing.SwingWorker.run(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    java.lang.Thread.run(Unknown Source)

Both files are attached here, thanks in advance.