Previously, when the message of the "with" operator can not be
accessed by the user, it used to return messages in combined feed
or stream feed.
This commit updates it to rather raise a BadNarrowOperatorError
if the message of "with" operand is not accessible to user, and the
narrow terms present can not define a conversation. However, if
the narrow terms can define a conversation, then the narrow falls
back to that of without the "with" operator.
8aad10b720