src: fix compiler warning for debug build

This commit updates the check of the offset argument passed to
CallJSOnreadMethod to avoid doing a cast as this currently generates
the following compiler warning when doing a debug build:

./src/stream_base.cc:295:3:
warning: comparison of integers of different signs:
'int32_t' (aka 'int') and 'size_t' (aka 'unsigned long')
[-Wsign-compare]
  CHECK_EQ(static_cast<int32_t>(offset), offset);
  ^        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ~~~~~~

src/stream_base.cc

@@ -292,7 +292,7 @@ void StreamBase::CallJSOnreadMethod(ssize_t nread,
 
 #ifdef DEBUG
   CHECK_EQ(static_cast<int32_t>(nread), nread);
-  CHECK_EQ(static_cast<int32_t>(offset), offset);
+  CHECK_LE(offset, INT32_MAX);
 
   if (ab.IsEmpty()) {
     CHECK_EQ(offset, 0);