qtmux: Error out on discontinuities/gaps when muxing raw audio

qtmux: Error out on discontinuities/gaps when muxing raw audio

When muxing raw audio, we have no way of storing timestamps but are just
storing a continuous stream of audio samples. If the difference between
the expected and the real timestamp becomes to big, we should error out
instead of silently creating files with wrong A/V sync.

https://bugzilla.gnome.org/show_bug.cgi?id=780679