bashcompinit incorrectly calculates COMP_LINE (proposed fix included)

[Evan Underscore <evanunderscore@xxxxxxxxx>]

Hi all,

A user discovered a bug in bashcompinit that causes COMP_LINE to be
incorrectly calculated. A summary of the incorrect behaviour is here:
https://github.com/kislyuk/argcomplete/issues/228#issuecomment-327696251
(Note some of the surrounding discussion is incorrect - this bug is
unrelated to unicode.) The table at the bottom of this comment summarises
how bashcompinit differs in its calculation of COMP_POINT.

The change that caused the bug appears to have been introduced here:
https://github.com/zsh-users/zsh/commit/23907bb840c80eef99eabba17e086e44c9b2d3fc#diff-b8d49b00032bcbfcdc709649f5d68505R11

Reverting this line (i.e. using CURRENT-1 instead of CURRENT, as it was
before this commit) fixes the bug for me, causing zsh to report 18 and 19
for the two test lines respectively, matching Bash.

I am not a subscriber; please send responses to this email address. I wish
to note the resolution of this on the argcomplete ticket.

Thanks,

Evan.