avcodec/lagarith: Sanity check scale

A value of 24 and above can collaps the range to 0 which would not work.

Fixes: Timeout (75sec -> 21sec)
Fixes: 18707/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LAGARITH_fuzzer-5708950892969984

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/lagarith.c

@@ -226,6 +226,9 @@ static int lag_read_prob_header(lag_rac *rac, GetBitContext *gb)
         }
     }
 
+    if (scale_factor > 23)
+        return AVERROR_INVALIDDATA;
+
     rac->scale = scale_factor;
 
     /* Fill probability array with cumulative probability for each symbol. */