Fix M5's locking problem: don't release a lock which you didn't create yourself, or better: don't touch it at all.
Fix M5's locking problem: don't release a lock which you didn't create
yourself, or better: don't touch it at all.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb