Fix a bunch of sign mismatch warnings.

core/src/fxcodec/codec/fx_codec_jpeg.cpp

Index: core/src/fxcodec/codec/fx_codec_jpeg.cpp
diff --git a/core/src/fxcodec/codec/fx_codec_jpeg.cpp b/core/src/fxcodec/codec/fx_codec_jpeg.cpp
index efd83f88ae5760b47a829bc1a9dd023450848e18..4fdbb8ed293b8f29d10db1035d98ee42b651e01a 100644
--- a/core/src/fxcodec/codec/fx_codec_jpeg.cpp
+++ b/core/src/fxcodec/codec/fx_codec_jpeg.cpp
@@ -193,7 +193,7 @@ static void _JpegEncode(const CFX_DIBSource* pSource,
     if (nComponents > 1) {
       uint8_t* dest_scan = line_buf;
       if (nComponents == 3) {
-        for (int i = 0; i < width; i++) {
+        for (FX_DWORD i = 0; i < width; i++) {
           dest_scan[0] = src_scan[2];
           dest_scan[1] = src_scan[1];
           dest_scan[2] = src_scan[0];
@@ -201,7 +201,7 @@ static void _JpegEncode(const CFX_DIBSource* pSource,
           src_scan += Bpp;
         }
       } else {
-        for (int i = 0; i < pitch; i++) {
+        for (FX_DWORD i = 0; i < pitch; i++) {
           *dest_scan++ = ~*src_scan++;
         }
       }