hlssink doesnt fragment audio-only streams

Submitted by Javier Jardón @jjardon

Link to original bug (#710203)

Description

Test case:

gst-launch-1.0 audiotestsrc ! faac ! mpegtsmux ! hlssink target-duration=2

doesnt generate new segments, while

gst-launch-1.0 videotestsrc ! x264enc ! mpegtsmux ! hlssink target-duration=2

works without problems