bitstring: fix bug in jive_bitstring_init_signed
bitstring: fix bug in jive_bitstring_init_signed

If the bitstring was greater than 64 bits, the upper bits were not
set to '1'.

Signed-off-by: Helge Bahmann <c5618920f622561f9c0ec5c42219c4c08180149f@chaoticmind.net>

phate/jive,phate/jive,phate/jive