Minimal fix for CVE-2020-8927

diff --git a/c/dec/bit_reader.h b/c/dec/bit_reader.h
index c06e914..4eff695 100644
--- a/c/dec/bit_reader.h
+++ b/c/dec/bit_reader.h
@@ -87,8 +87,11 @@ static BROTLI_INLINE uint32_t BrotliGetAvailableBits(
 }
 
 /* Returns amount of unread bytes the bit reader still has buffered from the
-   BrotliInput, including whole bytes in br->val_. */
+   BrotliInput, including whole bytes in br->val_. Result is capped with
+   maximal ring-buffer size (larger number won't be utilized anyway). */
 static BROTLI_INLINE size_t BrotliGetRemainingBytes(BrotliBitReader* br) {
+  static const size_t kCap = (size_t)1 << BROTLI_LARGE_MAX_WBITS;
+  if (br->avail_in > kCap) return kCap;
   return br->avail_in + (BrotliGetAvailableBits(br) >> 3);
 }