lavfi/avfilter: use av_assert

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/avfilter.c

@@ -139,7 +139,7 @@ int avfilter_link(AVFilterContext *src, unsigned srcpad,
     link->srcpad  = &src->output_pads[srcpad];
     link->dstpad  = &dst->input_pads[dstpad];
     link->type    = src->output_pads[srcpad].type;
-    assert(PIX_FMT_NONE == -1 && AV_SAMPLE_FMT_NONE == -1);
+    av_assert0(PIX_FMT_NONE == -1 && AV_SAMPLE_FMT_NONE == -1);
     link->format  = -1;
 
     return 0;