Fix JBig2 decoding logic

core/fxcodec/jbig2/JBig2_TrdProc.cpp

 // Copyright 2015 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fxcodec/jbig2/JBig2_TrdProc.h"
 
 #include <memory>
 
 #include "core/fxcodec/jbig2/JBig2_ArithDecoder.h"
 #include "core/fxcodec/jbig2/JBig2_ArithIntDecoder.h"
 #include "core/fxcodec/jbig2/JBig2_GrrdProc.h"
 #include "core/fxcodec/jbig2/JBig2_HuffmanDecoder.h"
 
 CJBig2_Image* CJBig2_TRDProc::decode_Huffman(CJBig2_BitStream* pStream,
                                              JBig2ArithCtx* grContext) {
   std::unique_ptr<CJBig2_HuffmanDecoder> pHuffmanDecoder(
       new CJBig2_HuffmanDecoder(pStream));
   std::unique_ptr<CJBig2_Image> SBREG(new CJBig2_Image(SBW, SBH));
   SBREG->fill(SBDEFPIXEL);
   int32_t STRIPT;
   if (pHuffmanDecoder->decodeAValue(SBHUFFDT, &STRIPT) != 0)
     return nullptr;
 
   STRIPT *= SBSTRIPS;
   STRIPT = -STRIPT;
+  int32_t FIRSTS = 0;
   uint32_t NINSTANCES = 0;
   while (NINSTANCES < SBNUMINSTANCES) {
     int32_t DT;
     if (pHuffmanDecoder->decodeAValue(SBHUFFDT, &DT) != 0)
       return nullptr;
 
     DT *= SBSTRIPS;
     STRIPT = STRIPT + DT;
     bool bFirst = true;
-    int32_t FIRSTS = 0;
     int32_t CURS = 0;
     for (;;) {
       if (bFirst) {
         int32_t DFS;
         if (pHuffmanDecoder->decodeAValue(SBHUFFFS, &DFS) != 0)
           return nullptr;
 
         FIRSTS = FIRSTS + DFS;
         CURS = FIRSTS;
         bFirst = false;
@@ skipping 350 matching lines @@
         CURS += WI - 1;
       } else if (TRANSPOSED == 1 && ((REFCORNER == JBIG2_CORNER_TOPLEFT) ||
                                      (REFCORNER == JBIG2_CORNER_TOPRIGHT))) {
         CURS += HI - 1;
       }
       ++NINSTANCES;
     }
   }
   return SBREG.release();
 }