avcodec/bonk: decode multiple passes in intlist_read() at once

This makes the worst case much faster

Fixes: Timeout
Fixes: 51363/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BONK_fuzzer-5660734784143360
Fixes: 57957/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BONK_fuzzer-5874095467397120

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

libavcodec/bonk.c

@@ -155,6 +155,7 @@ static int intlist_read(BonkContext *s, int *buf, int entries, int base_2_part)
     int n_zeros = 0, step = 256, dominant = 0;
     int pos = 0, level = 0;
     BitCount *bits = s->bits;
+    int passes = 1;
 
     memset(buf, 0, entries * sizeof(*buf));
     if (base_2_part) {
@@ -216,24 +217,28 @@ static int intlist_read(BonkContext *s, int *buf, int entries, int base_2_part)
     x = 0;
     n_zeros = 0;
     for (i = 0; n_zeros < entries; i++) {
+        if (x >= max_x)
+            return AVERROR_INVALIDDATA;
+
         if (pos >= entries) {
             pos = 0;
-            level += 1 << low_bits;
+            level += passes << low_bits;
+            passes = 1;
+            if (bits[x].bit && bits[x].count > entries - n_zeros)
+                passes =  bits[x].count / (entries - n_zeros);
         }
 
         if (level > 1 << 16)
             return AVERROR_INVALIDDATA;
 
-        if (x >= max_x)
-            return AVERROR_INVALIDDATA;
-
         if (buf[pos] >= level) {
             if (bits[x].bit)
-                buf[pos] += 1 << low_bits;
+                buf[pos] += passes << low_bits;
             else
                 n_zeros++;
 
-            bits[x].count--;
+            av_assert1(bits[x].count >= passes);
+            bits[x].count -= passes;
             x += bits[x].count == 0;
         }