Fix buffer size offset error in PNG_Predictor

BUG=393602
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/466153005

core/src/fxcodec/codec/fx_codec_flate.cpp

diff --git a/core/src/fxcodec/codec/fx_codec_flate.cpp b/core/src/fxcodec/codec/fx_codec_flate.cpp
index c02f097..a12fffb 100644
--- a/core/src/fxcodec/codec/fx_codec_flate.cpp
+++ b/core/src/fxcodec/codec/fx_codec_flate.cpp
@@ -398,6 +398,7 @@
     FX_LPBYTE pDestData = dest_buf;
     for (int row = 0; row < row_count; row ++) {
         FX_BYTE tag = pSrcData[0];
+        byte_cnt++;
         if (tag == 0) {
             int move_size = row_size;
             if ((row + 1) * (move_size + 1) > (int)data_size) {
@@ -406,7 +407,7 @@
             FXSYS_memmove32(pDestData, pSrcData + 1, move_size);
             pSrcData += move_size + 1;
             pDestData += move_size;
-            byte_cnt += move_size + 1;
+            byte_cnt += move_size;
             continue;
         }
         for (int byte = 0; byte < row_size && byte_cnt < (int)data_size; byte ++) {
@@ -464,7 +465,6 @@
         }
         pSrcData += row_size + 1;
         pDestData += row_size;
-        byte_cnt++;
     }
     FX_Free(data_buf);
     data_buf = dest_buf;