add range checks on byte length to bit length calculation

[Brian Campbell]

check that the input byte length is non negative and won't result in an integer overflow

[Brian Campbell]

fix #98 with a range checks (non negative and won't result in an integer overflow) on byte length to bit length calculation

→ <<cset b79e67c13c23>>

[Brian Campbell]

in v0.5.7

[Brian Campbell]

borrowed test case from Quan Nguyen via https://bitbucket.org/connect2id/nimbus-jose-jwt/issues/224/byte-to-bit-overflow-in-cbc