BUG/MINOR: hlua: Don't strip last non-LWS char in hlua_pushstrippedstring()

BUG/MINOR: hlua: Don't strip last non-LWS char in hlua_pushstrippedstring()

hlua_pushstrippedstring() function strips leading and trailing LWS
characters. But the result length it too short by 1 byte. Thus the last
non-LWS character is stripped. Note that a string containing only LWS
characters resulting to a stipped string with an invalid length (-1). This
leads to a lua runtime error.

This bug was reported in the issue #1155. It must be backported as far as
1.7.

(cherry picked from commit 2ec4e3c1acf95bcdc56028bbefe1a355c457b978)
Signed-off-by: Willy Tarreau <w@1wt.eu>