Clarify error message on empty range selector

[MattiSG]

When I use a selector that has an empty intersection, for example because the endBefore is before the startBefore, I get the following error:

     ExtractDocumentError: Extract failed: The provided selector "[object Object]" has no match in the web page at 'https://example.com'

It is unclear if one of the two range ends selector does not match, is misspelled, or if the intersection is empty.