The hasSingleUnnamedParam function was only checking the parameter type
but not whether the parameter actually had no name. This caused functions
with a single NAMED parameter (e.g., `foo(data json)`) to incorrectly
match the single-param fallback mode.
The result was a confusing PostgreSQL error 42883 "function does not exist"
instead of a clean PGRST202 error explaining that no matching function
was found.
Added ppName == mempty check so functions with named parameters don't
incorrectly match the single-param fallback.
(cherry picked from commit fd6a3bdccf)
