Always lock dbb_sync before accessing something in setLockAttachment()

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58498 65644016-39b1-43b1-bf79-96bc8fe82c15
Postfix for CORE-3935 & CORE-3944: helps avoid segfaults/deadlocks when shutting down firebird

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@58499 65644016-39b1-43b1-bf79-96bc8fe82c15