Consider the following message S1(S2(M)).
1. S1 contains a two different SignerInfos. SignerInfo #1 cannot be
validated and contains an MLA Expansion history element. SignerInfo #2
can be validated. Does the MLA stop processing of the message? This is
the case if there were two different MLA Expansion history elements, but
this case is not explicity addressed.
2. S1 validates and contains an MLA Expansion history element. S2
fails validation. Since the MLA could in theory just evaluate S1 and
not look at S2, is it considered to be illeagle behavior (i.e. MUST stop
processing) to pass on this message?