MFC: r261773

In acline_init(), initialize ac_line to SRC_UNKNOWN.  Previously
this could lead to the -n option effectively being ignored (in case
ac_line happened to be 0 aka SRC_AC), or other undefined behaviour.

PR:		169779
Submitted by:	Alex Gonzalez <loox at e-shell.com>
Reviewed by:	jhb
Merge remote-tracking branch 'upstream-github/stable/9' into stable/9