Comment 2 for bug 841966

StacktraceTop:
 g_str_has_prefix (str=0x0, prefix=0x7fe5f2e9727d "cdda://") at /build/buildd/glib2.0-2.29.18/./glib/gstrfuncs.c:2943
 set_source_properties (playback_mode=1, uri=0x0, source=0x31fe320) at rb-audiocd-plugin.c:107
 rb_audiocd_plugin_prepare_player_source_cb (player=<optimized out>, stream_uri=0x0, source=<optimized out>, plugin=<optimized out>) at rb-audiocd-plugin.c:140
 g_closure_invoke (closure=0x2d581a0, return_value=0x0, n_param_values=3, param_values=0x2027450, invocation_hint=<optimized out>) at /build/buildd/glib2.0-2.29.18/./gobject/gclosure.c:774
 signal_emit_unlocked_R (node=<optimized out>, detail=0, instance=0x1d82260, emission_return=0x0, instance_and_params=0x2027450) at /build/buildd/glib2.0-2.29.18/./gobject/gsignal.c:3272