fix internal buffer overrun in inet_pton

fix internal buffer overrun in inet_pton

one stop condition for parsing abbreviated ipv6 addressed was missed,
allowing the internal ip[] buffer to overflow. this patch adds the
missing stop condition and masks the array index so that, in case
there are any remaining stop conditions missing, overflowing the
buffer is not possible.

(cherry picked from commit fc13acc3dcb5b1f215c007f583a63551f6a71363)