Slightly changed the invariant handling code for functions.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59117 65644016-39b1-43b1-bf79-96bc8fe82c15
Fixed CORE-4304 - Engine crashes when attempt to REcreate table with FK after syntax error before such recreating.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59118 65644016-39b1-43b1-bf79-96bc8fe82c15