[DomCrawler] Fixed a forgotten case of complex XPath queries

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10986
| License       | MIT
| Doc PR        | n/a

This fixes the case I forgot when rewritting the XPath to avoid making it produce invalid queries. I ran the new tests against the old implementation first, to ensure they cover the BC properly.

I could have detected it by running the Mink 1.5 testsuite with the new code (which is the case for people reporting the bug), but I only ran it for Mink 1.6 which does not produce such XPath anymore.