MultiReadSeeker returns a ReadSeeker that's the logical concatenation of the provided
input readseekers. After calling this method the initial position is set to the
beginning of the first ReadSeeker. At the end of a ReadSeeker, Read always advances
to the beginning of the next ReadSeeker and returns EOF at the end of the last ReadSeeker.
Seek can be used over the sum of lengths of all readseekers.
When a MultiReadSeeker is used, no Read and Seek operations should be made on
its ReadSeeker components. Also, users should make no assumption on the state
of individual readseekers while the MultiReadSeeker is used.