Restore zero-initialization of message items flagged as NULLs.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@60077 65644016-39b1-43b1-bf79-96bc8fe82c15
Fix padding of UNICODE_FSS - complement to CORE-3431 (UTF-8) fix.

Hope this does not cause a lot of ISQL-based tests to fail.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@60078 65644016-39b1-43b1-bf79-96bc8fe82c15