isEmptyObject check is uncareful

[LewisJEllis]

It has a for key in obj without a if (obj.hasOwnProperty(key)) here.

Actual impact is relatively small; if there's a polluted global object prototype, we might send empty objects when we'd otherwise discard them, and (main concern) we might include a breadcrumb when breadcrumbCallback told us not to.

[mattrobenolt]

You mad? f1c518d