Fix some code which causes warnings when compiled by /analyze tool

core/fxcodec/codec/fx_codec_png.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 <algorithm>
 
 #include "core/fxcodec/codec/codec_int.h"
 #include "core/fxcodec/include/fx_codec.h"
@@ skipping 38 matching lines @@
     png_get_iCCP(png_ptr, info_ptr, &icc_name, &compress_type, &icc_profile,
                  &icc_proflen);
 #endif
     int bTime = 0;
 #if defined(PNG_tIME_SUPPORTED)
     png_timep t = NULL;
     png_get_tIME(png_ptr, info_ptr, &t);
     if (t) {
       FXSYS_memset(pAttribute->m_strTime, 0, sizeof(pAttribute->m_strTime));
       FXSYS_snprintf((FX_CHAR*)pAttribute->m_strTime,
-                     sizeof(pAttribute->m_strTime), "%4d:%2d:%2d %2d:%2d:%2d",
+                     sizeof(pAttribute->m_strTime), "%4u:%2u:%2u %2u:%2u:%2u",
                      t->year, t->month, t->day, t->hour, t->minute, t->second);
       pAttribute->m_strTime[sizeof(pAttribute->m_strTime) - 1] = 0;
       bTime = 1;
     }
 #endif
 #if defined(PNG_TEXT_SUPPORTED)
     int i;
     FX_STRSIZE len;
     const FX_CHAR* buf;
     int num_text;
@@ skipping 177 matching lines @@
   if (setjmp(png_jmpbuf(ctx->png_ptr))) {
     if (pAttribute &&
         0 == FXSYS_strcmp(m_szLastError, "Read Header Callback Error")) {
       _png_load_bmp_attribute(ctx->png_ptr, ctx->info_ptr, pAttribute);
     }
     return FALSE;
   }
   png_process_data(ctx->png_ptr, ctx->info_ptr, (uint8_t*)src_buf, src_size);
   return TRUE;
 }