avfilter/avfiltergraph: Clear graph pointers in ff_filter_graph_remove_filter()

When a filter is no longer part of a graph, its pointers should be cleared
so no stale pointers remain.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/avfiltergraph.c

@@ -93,12 +93,17 @@ AVFilterGraph *avfilter_graph_alloc(void)
 
 void ff_filter_graph_remove_filter(AVFilterGraph *graph, AVFilterContext *filter)
 {
-    int i;
+    int i, j;
     for (i = 0; i < graph->nb_filters; i++) {
         if (graph->filters[i] == filter) {
             FFSWAP(AVFilterContext*, graph->filters[i],
                    graph->filters[graph->nb_filters - 1]);
             graph->nb_filters--;
+            filter->graph = NULL;
+            for (j = 0; j<filter->nb_outputs; j++)
+                if (filter->outputs[j])
+                    filter->outputs[j]->graph = NULL;
+
             return;
         }
     }