stop running processes

[pawaom]

the issue with stopping a running process is disused in a similar library

https://github.com/WritingMinds/ffmpeg-android-java/issues/79

please update the file ffmpeg.java

@Override
    public boolean isCommandRunning(FFtask task) {
        return task != null && !task.isProcessCompleted();
    }

    @Override
    public boolean killRunningProcesses(FFtask task) {
        return task != null && task.killRunningProcess();
    }

to 

@Override
    public boolean isCommandRunning(FFtask task) {
        return task != null ||  !task.isProcessCompleted();
    }

    @Override
    public boolean killRunningProcesses(FFtask task) {
        return task != null || task.killRunningProcess();
    }