Make avfilter_graph_add_filter() returns AVERROR(ENOMEM) in case of

failed reallocation, rather than just -1.

Originally committed as revision 22878 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/avfiltergraph.c

@@ -40,7 +40,7 @@ int avfilter_graph_add_filter(AVFilterGraph *graph, AVFilterContext *filter)
                                 sizeof(AVFilterContext*) * ++graph->filter_count);
 
     if (!graph->filters)
-        return -1;
+        return AVERROR(ENOMEM);
 
     graph->filters[graph->filter_count - 1] = filter;