BUG/MINOR: lua: In error case, the safe mode is not removed

Just forgot of reset the safe mode. This have not consequences
the safe mode just set a pointer on fucntion which is called only
and initialises a longjmp.

Out of lua execution, this longjmp is never executed and the
function is never called.

This patch should be backported in 1.6 and 1.7
diff --git a/src/hlua.c b/src/hlua.c
index 85e0c66..408a9f2 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -857,6 +857,7 @@
 	lua->T = lua_newthread(gL.T);
 	if (!lua->T) {
 		lua->Tref = LUA_REFNIL;
+		RESET_SAFE_LJMP(gL.T);
 		return 0;
 	}
 	hlua_sethlua(lua);