Attempted to fix a possible crash due to the wrong request pointer remaining in tdbb after sub-request execution. While being there, cleaned up some redundant code.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58206 65644016-39b1-43b1-bf79-96bc8fe82c15
The first fix for CORE-4123: Firebird crash when executing an stored procedure called by a trigger that converts string to upper.
Adriano, please review. BTW, I'm far not sure that other TextType members (those calling texttype_fn_* routines from INTL) cannot silently return "special" return codes either.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/branches/B2_5_Release@58211 65644016-39b1-43b1-bf79-96bc8fe82c15