n-api: fix TypedAarray info for ArrayBuffer offset

The JsGetTypedArrayStorage API returns a buffer pointer that already
incorporates the offset into the ArrayBuffer, so adding the offset
was a mistake.

This bug was caught by the N-API C++ wrapper tests at
https://github.com/nodejs/node-addon-api/blob/master/test/typedarray.js

PR-URL: nodejs#259
Reviewed-By: Hitesh Kanwathirtha <[email protected]>
Reviewed-By: Kunal Pathak <[email protected]>
Reviewed-By: Taylor Woll <[email protected]>
Reviewed-By: Kyle Farnung <[email protected]>

src/node_api_jsrt.cc

@@ -1995,7 +1995,7 @@ napi_status napi_get_typedarray_info(napi_env env,
   }
 
   if (data != nullptr) {
-    *data = static_cast<uint8_t*>(bufferData) + byteOffset;
+    *data = static_cast<uint8_t*>(bufferData);
   }
 
   if (arraybuffer != nullptr) {