Suggestion: add method for QReadWriteLock to check if unlock() will succeed and not cause error

According to documentation, "Attempting to unlock a lock that is not locked is an error, and will result in program termination."

It would be nice if the user could check if QReadWriteLock will succeed with the unlock() operation. Maybe a function like getState() which would return a (lockedForWrite,lockedForRad,unlocked) could be implemented.