fixed bug that caused the psk encoder to pad too many 0s (factor 8)

(added one item for every 0 bit, instead of one for every 0 byte)

note that if the number of 0s that should be padded is not a multiple
of 8, the block still adds up to 7 excessive 0s, as the block
can currently only produce full bytes of data.
However, this may be inevitable anyways, as the modulator also expects
a byte stream as input