chakrashim: Fixing v8::ArrayBuffer implementation detail

v8::ArrayBuffer was returning raw internal pointers to ArrayBuffers.
This is fine in general, but in v8 in particular these pointers are
guaranteed to be non-null. For chakracore in the case of empty ArrayBuffers
this implicit assumption was broken, which showed up in one test scenario

We now explicitly check for this case and return a valid (if useless) pointer
instead.

deps/chakrashim/src/v8arraybuffer.cc

@@ -105,6 +105,16 @@ ArrayBuffer::Contents ArrayBuffer::GetContents() {
   }
 
   Contents contents;
+  if (buffer == nullptr)
+  {
+    CHAKRA_ASSERT(bufferLength == 0);
+    // v8's version of ArrayBuffer will return a non-null pointer even in the case of
+    // an empty ArrayBuffer, and this behavior is relied upon by some of the i18n code.
+    // To support that, if we would otherwise return a null buffer, as long as the
+    // length is 0 we instead return a valid pointer to something, on the understanding
+    // that nobody will actually try to read it.
+    buffer = (BYTE*)this;
+  }
   contents.data_ = buffer;
   contents.byte_length_ = bufferLength;
   return contents;