Fix infinite loop in GetBestLengths

When compressing a file with a large run of repeated bytes, ECT could
skip full match finding without updating the match finder binary tree
correctly. This could lead to a rare infinite loop in match finding.

Author: fhanau

src/LzFind.c

@@ -377,7 +377,9 @@ void Bt3Zip_MatchFinder_Skip(CMatchFinder* p, UInt32 num)
   }
 }
 
-//Same as above, but optimized for case where there is a ZOPFLI_MAX_MATCH len match at distance 1.
+// Same as above, but optimized for case where there is a ZOPFLI_MAX_MATCH len match at distance 1.
+// This implies that the match finder has processed at least one byte so far – otherwise there
+// can't be available matches.
 void Bt3Zip_MatchFinder_Skip2(CMatchFinder* p, UInt32 num)
 {
   const Byte *cur = p->buffer;

src/zopfli/squeeze.c

@@ -568,7 +568,7 @@ static void GetBestLengths(const ZopfliOptions* options, const unsigned char* in
               memset(p.hash, 0, LZFIND_HASH_SIZE * sizeof(unsigned));
               p.cyclicBufferPos = 0;
               p.pos = ZOPFLI_WINDOW_SIZE;
-              Bt3Zip_MatchFinder_Skip2(&p, 1);
+              Bt3Zip_MatchFinder_Skip(&p, 1);
             }
             else {
               Bt3Zip_MatchFinder_Skip2(&p, match);