avdevice/lavfi: Use avio_closep() to avoid leaving stale pointers in memory

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

libavdevice/lavfi.c

@@ -147,7 +147,7 @@ av_cold static int lavfi_read_header(AVFormatContext *avctx)
             goto end;
         av_bprint_init(&graph_file_pb, 0, AV_BPRINT_SIZE_UNLIMITED);
         ret = avio_read_to_bprint(avio, &graph_file_pb, INT_MAX);
-        avio_close(avio);
+        avio_closep(&avio);
         av_bprint_chars(&graph_file_pb, '\0', 1);
         if (!ret && !av_bprint_is_complete(&graph_file_pb))
             ret = AVERROR(ENOMEM);