audio_mix: initialize the data pointers to NULL

This should make it easier to catch problems where some of those
pointers are used uninitialized, since reading from NULL should always
crash, while random numbers from stack can turn out to be valid
pointers, so random memory may be silently overwritten.

libavresample/audio_mix.c

@@ -447,7 +447,7 @@ int ff_audio_mix(AudioMix *am, AudioData *src)
 
     if (am->in_matrix_channels && am->out_matrix_channels) {
         uint8_t **data;
-        uint8_t *data0[AVRESAMPLE_MAX_CHANNELS];
+        uint8_t *data0[AVRESAMPLE_MAX_CHANNELS] = { NULL };
 
         if (am->out_matrix_channels < am->out_channels ||
              am->in_matrix_channels <  am->in_channels) {