Fixed the issue privately reported by Claudio.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59580 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed CORE-4422: FB crashes when using row_number()over( PARTITION BY x) in ORDER by clause. Adriano, please review.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59581 65644016-39b1-43b1-bf79-96bc8fe82c15