[MONDRIAN-1568] Fixing failure due to infinite loop while determining aggregate star

Looking up the agg star when role-limited members are in context requires finding the set of accessible members in order to set the complete bitkey.  Determining those members when using a context constraint requires looking up the agg star.  

To side-step the issue, set NonEmpty to false when looking for accessible members while setting
the constraintBitKey, which avoids use of a context constraint.