Re-enable warning 4701 for GN build and some cleanup

core/fxcodec/jbig2/JBig2_Context.cpp

 // Copyright 2014 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_Context.h"
 
 #include <algorithm>
 #include <list>
@@ skipping 1267 matching lines @@
   int32_t runcodes[kRunCodesSize];
   int32_t runcodes_len[kRunCodesSize];
   for (size_t i = 0; i < kRunCodesSize; ++i) {
     if (pStream->readNBits(4, &runcodes_len[i]) != 0)
       return nullptr;
   }
   huffman_assign_code(runcodes, runcodes_len, kRunCodesSize);
 
   std::unique_ptr<JBig2HuffmanCode, FxFreeDeleter> SBSYMCODES(
       FX_Alloc(JBig2HuffmanCode, SBNUMSYMS));
-  int32_t run;
+  int32_t run = 0;
   int32_t i = 0;
   while (i < (int)SBNUMSYMS) {
     size_t j;
     int32_t nVal = 0;
     int32_t nBits = 0;
     uint32_t nTemp;
     while (true) {
       if (pStream->read1Bit(&nTemp) != 0)
         return nullptr;
 
@@ skipping 107 matching lines @@
         SBSYMCODES[CURTEMP].code = CURCODE;
         CURCODE = CURCODE + 1;
       }
       CURTEMP = CURTEMP + 1;
     }
     CURLEN = CURLEN + 1;
   }
   FX_Free(LENCOUNT);
   FX_Free(FIRSTCODE);
 }