More Windows 64b compilation warning fixes

src/images/bmpdecoderhelper.cpp

Index: src/images/bmpdecoderhelper.cpp
===================================================================
--- src/images/bmpdecoderhelper.cpp	(revision 12322)
+++ src/images/bmpdecoderhelper.cpp	(working copy)
@@ -18,7 +18,7 @@
 static const int kMaxDim = SHRT_MAX / 2;
 
 bool BmpDecoderHelper::DecodeImage(const char* p,
-                                   int len,
+                                   size_t len,
                                    int max_pixels,
                                    BmpDecoderCallback* callback) {
   data_ = reinterpret_cast<const uint8*>(p);
@@ -153,7 +153,7 @@
     rowLen += rowPad_;
   }
 
-  if (offset > 0 && offset > pos_ && offset < len_) {
+  if (offset > 0 && (size_t)offset > pos_ && (size_t)offset < len_) {
     pos_ = offset;
   }
   // Deliberately off-by-one; a load of BMPs seem to have their last byte
@@ -182,7 +182,7 @@
   static const uint8 RLE_DELTA = 2;
   int x = 0;
   int y = height_ - 1;
-  while (pos_ < len_ - 1) {
+  while (pos_ + 1 < len_) {
     uint8 cmd = GetByte();
     if (cmd != RLE_ESCAPE) {
       uint8 pixels = GetByte();
@@ -210,7 +210,7 @@
           return;
         }
       } else if (cmd == RLE_DELTA) {
-        if (pos_ < len_ - 1) {
+        if (pos_ + 1 < len_) {
           uint8 dx = GetByte();
           uint8 dy = GetByte();
           x += dx;
@@ -336,7 +336,7 @@
 }
 
 uint8 BmpDecoderHelper::GetByte() {
-  CHECK(pos_ >= 0 && pos_ <= len_);
+  CHECK(pos_ <= len_);
   // We deliberately allow this off-by-one access to cater for BMPs with their
   // last byte missing.
   if (pos_ == len_) {