Jan Weber

Fixes gstreamer-java/gst1-java-core#270

WebRTCBin.createAnswer() callback not called sporadically (promise garbage collected)

4

Looks like the promise which is used inside the method sometimes gets garbage collected before callback is called. reproducible with: ``` webRtcBin.createAnswer(answer -> { System.out.println("ANSWER"); }); System.gc(); ```