Fixing issue causing Issue.isOpen() to always return false

Both the condition and the equality function used were wrong, the code
expected to return true if the issue's current state was "closed"
instead of "open" and instead of using String.equals(..) it was using
the reference equality operator "=="
The current implementation will return true only when the issue current
state equals "open", this means that it may return false even for states
that are not "closed" (e.g., null)