BUG/MINOR: state-file: do not leak memory on parse errors

BUG/MINOR: state-file: do not leak memory on parse errors

Issue #417 reports a possible memory leak in the state-file loading code.
There's one such place in the loop which corresponds to parsing errors
where the curreently allocated line is not freed when dropped. In any
case this is very minor in that no more than the file's length may be
lost in the worst case, considering that the whole file is kept anyway
in case of success. This fix addresses this.

It should be backported to 2.1.

(cherry picked from commit ca7a5af664504cbe13240e5bc538efbcef4f6162)
Signed-off-by: Willy Tarreau <w@1wt.eu>