Fix missing audio tracks.

 * https://bugzilla.rpmfusion.org/show_bug.cgi?id=6006
 * https://github.com/HandBrake/HandBrake/commit/f28289fb06ab461ea082b4be56d6d1504c0c31c2

Index: libhb/encavcodecaudio.c
--- libhb/encavcodecaudio.c.orig
+++ libhb/encavcodecaudio.c
@@ -409,7 +409,10 @@ static void Encode(hb_work_object_t *w, hb_buffer_list
 
         // Prepare input frame
         int     out_size;
-        AVFrame frame = { .nb_samples = pv->samples_per_frame, };
+        AVFrame frame = { .nb_samples = pv->samples_per_frame,
+                          .format = pv->context->sample_fmt,
+                          .channels = pv->context->channels
+        };
 
         out_size = av_samples_get_buffer_size(NULL,
                                               pv->context->channels,
