Return at what position the latest underflow occurred, or -1 if this information is not
* known (e.g.\ if no underflow has occurred, or server is older than 1.0).
* Can be used inside the underflow callback to get information about the current underflow.
* (Only for playback streams) \since 1.0
Return at what position the latest underflow occurred, or -1 if this information is not * known (e.g.\ if no underflow has occurred, or server is older than 1.0). * Can be used inside the underflow callback to get information about the current underflow. * (Only for playback streams) \since 1.0