tsf_channel_get_pan is reporting pan - 1

Hi!

I'm pretty sure this is just an issue with a flipped sign.
Current pseudocode:

**tsf_channel_set_pan(pan)**
panOffset = pan - 0.5f

**tsf_channel_get_pan()**
return panOffset - 0.5f // equals pan - 0.5 - 0.5

Changing tsf_channel_get_pan to return panOffset **+** 0.5f fixes it.

<3