BUG: Fix error when unpacking messages with v1 header
BUG: Fix error when unpacking messages with v1 header

When unpacking a message with a v1 header, igtlMessageBase::UnpackHeader attempted to unpack the extended header and metadata. This resulted in failure since neither are valid for v1 headers.

Fixed by only attempting to unpack the extended header and metadata for header version >= 2.

openigtlink/OpenIGTLink,openigtlink/OpenIGTLink,openigtlink/OpenIGTLink,openigtlink/OpenIGTLink,openigtlink/OpenIGTLink