avfilter/vf_stack: free input pads name on uninit

Signed-off-by: NPaul B Mahol <onemda@gmail.com>

libavfilter/vf_stack.c

@@ -215,8 +215,13 @@ static int request_frame(AVFilterLink *outlink)
 static av_cold void uninit(AVFilterContext *ctx)
 {
     StackContext *s = ctx->priv;
+    int i;
+
     ff_framesync_uninit(&s->fs);
     av_freep(&s->frames);
+
+    for (i = 0; i < ctx->nb_inputs; i++)
+        av_freep(&ctx->input_pads[i].name);
 }
 
 #define OFFSET(x) offsetof(StackContext, x)