Trivial fix for CORE-4500: Firebird crashes after unsuccessful remapping of the lock table's shared memory.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59927 65644016-39b1-43b1-bf79-96bc8fe82c15
Follow-up.

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59928 65644016-39b1-43b1-bf79-96bc8fe82c15
Cleanup and optimize locking a bit (as suggested by Dmitry)

git-svn-id: svn+ssh://svn.code.sf.net/p/firebird/code/firebird/trunk@59929 65644016-39b1-43b1-bf79-96bc8fe82c15