Continued Resource::Manger cleanup (JIRA RIPD-372)

 - Incorporates review comments from previous commit.
 - Increases Resource::Manager unit test coverage: verify a dropped consumer is blocked for a while.



or just 

if (m_logic && m_entry)

or even:

return (m_logic && m_entry) ? m_logic->charge(*m_entry, Charge(0)) : d;