raise a typed exception for unpacker when unknown secondary dex mode is encountered
raise a typed exception for unpacker when unknown secondary dex mode is encountered

Summary: Redex: adding this exception in order to distinguish this error in caller.

Reviewed By: thezhangwei

Differential Revision: D15071697

fbshipit-source-id: 92a23816aade06d3a54fcf673082415ab8582e28

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