Client library: fix handling of missing chunk and chunk server access, i.e. when lease acquire or lease renew info differs from get alloc, by forcing the lease re-acquisition and releasing the current lease only after successful lease re-acquisition. While it is possible to find out the chunk placement from the lease chunk server access, and avoid re-issuing get alloc, such optimization seem riskier at this time. Perhaps in the future the protocol will be changed to always use lease acquire instead of get alloc with and without authentication enabled.