Fixed races in legacy auth plugin

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58717 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed CORE-4247 - Delete "where current of" cursor fails for tables with newly added fields.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58718 65644016-39b1-43b1-bf79-96bc8fe82c15