Bugfix for onPlayBackStopped.

It has happened many times before that after stopping the player on the first few seconds/minutes, the file becomes unplayable afterwards. This is the log:

```
17:16:19 T:2890032192   ERROR: EXCEPTION Thrown (PythonToCppException) : -->Python callback/script returned the following error<--
                                             - NOTE: IGNORING THIS CAN LEAD TO MEMORY LEAKS!
                                            Error Type: <type 'exceptions.AttributeError'>
                                            Error Contents: 'player' object has no attribute 'currentTime'
                                            Traceback (most recent call last):
                                              File "/home/pi/.xbmc/addons/plugin.video.genesis/default.py", line 477, in onPlayBackStopped
                                                if self.currentTime / self.totalTime >= .9:
                                            AttributeError: 'player' object has no attribute 'currentTime'
                                            -->End of Python script error report<--
```

This pull-request should at least fix the AttributeError.