avfilter/af_compand: silence "maybe uninitialized" warnings

if channels is 0 it actually would be uninitialized, thus an assert with comment is added
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/af_compand.c

@@ -22,6 +22,7 @@
  *
  */
 
+#include "libavutil/avassert.h"
 #include "libavutil/avstring.h"
 #include "libavutil/opt.h"
 #include "libavutil/samplefmt.h"
@@ -214,9 +215,11 @@ static int compand_delay(AVFilterContext *ctx, AVFrame *frame)
     AVFilterLink *inlink = ctx->inputs[0];
     const int channels = inlink->channels;
     const int nb_samples = frame->nb_samples;
-    int chan, i, dindex, oindex, count;
+    int chan, i, av_uninit(dindex), oindex, av_uninit(count);
     AVFrame *out_frame = NULL;
 
+    av_assert1(channels > 0); /* would corrupt delay_count and delay_index */
+
     for (chan = 0; chan < channels; chan++) {
         const double *src = (double *)frame->data[chan];
         double *dbuf = (double *)s->delayptrs[chan];