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>
diff --git a/src/hlua_fcn.c b/src/hlua_fcn.c
index 06ff48d..7676d25 100644
--- a/src/hlua_fcn.c
+++ b/src/hlua_fcn.c
@@ -171,12 +171,13 @@
 const char *hlua_pushstrippedstring(lua_State *L, const char *str)
 {
 	const char *p;
-	const char *e;
+	int l;
 
 	for (p = str; HTTP_IS_LWS(*p); p++);
-	for (e = p + strlen(p) - 1; e > p && HTTP_IS_LWS(*e); e--);
+
+	for (l = strlen(p); l && HTTP_IS_LWS(p[l-1]); l--);
 
-	return lua_pushlstring(L, p, e - p);
+	return lua_pushlstring(L, p, l);
 }
 
 /* The three following functions are useful for adding entries