fftools/ffprobe: Loop over correct number of streams when flushing decoders

Some formats like FLV can dynamically add streams during packet reading.
FFprobe does check for this and reallocates the global stream info, but does
not reallocate InputFrame's streams and decoders when this happens, which,
as a result, could have caused flushing to occur on an out of bounds stream
index, since the flush loop iterates over fmt_ctx's nb_streams, and not
ifile's, despite using ifile's streams.

This fixes an out of bounds read and segfult.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

fftools/ffprobe.c

@@ -2893,7 +2893,7 @@ static int read_interval_packets(WriterContext *w, InputFile *ifile,
     }
     av_packet_unref(pkt);
     //Flush remaining frames that are cached in the decoder
-    for (i = 0; i < fmt_ctx->nb_streams; i++) {
+    for (i = 0; i < ifile->nb_streams; i++) {
         pkt->stream_index = i;
         if (do_read_frames) {
             while (process_frame(w, ifile, frame, pkt, &(int){1}) > 0);