Not reporting request params (for Sinatra?)

[tombruijn]

Describe the bug

We're not reporting request parameters for (at least) Sinatra apps since Ruby gem 3.9.0.

Probably related to #1100

Confirmed broken. This is because we now set params at the beginning of the request handling, instead of in the ensure block. If set beforehand, something happens with the parsing (possibly because POST payload processing happens in some middleware), and memoizes the request params as an empty Hash.

Solution: set if afterwards, which means a little rethink of how we set parameters.