avcodec/flac_parser: Raise threshold for detecting invalid data

Fixes regression from Ticket5428
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit b0b3676e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/flac_parser.c

@@ -617,8 +617,8 @@ static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx,
 
         if (!av_fifo_space(fpc->fifo_buf) &&
             av_fifo_size(fpc->fifo_buf) / FLAC_AVG_FRAME_SIZE >
-            fpc->nb_headers_buffered * 10) {
-            /* There is less than one valid flac header buffered for 10 headers
+            fpc->nb_headers_buffered * 20) {
+            /* There is less than one valid flac header buffered for 20 headers
              * buffered. Therefore the fifo is most likely filled with invalid
              * data and the input is not a flac file. */
             goto handle_error;