Closing methods should not interfere with returning values

A closing method cannot be called in its own stack slot, as there may
be returning values in the stack after that slot, and the call would
corrupt those values. Instead, the closing method must be copied to the
top of the stack to be called.

Moreover, even when a function returns no value, its return istruction
still has to have its position (which will set the stack top) after
the local variables, otherwise a closing method might corrupt another
not-yet-called closing method.

lvm.c

@@ -1452,7 +1452,8 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         vmbreak;
       }
       vmcase(OP_CLOSE) {
-        luaF_close(L, ra, LUA_OK);
+        L->top = ra + 1;  /* everything is free after this slot */
+        ProtectNT(luaF_close(L, ra, LUA_OK));
         vmbreak;
       }
       vmcase(OP_TBC) {
@@ -1619,13 +1620,14 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
           n = cast_int(L->top - ra);  /* get what is available */
         else
           L->top = ra + n;  /* set call for 'luaD_poscall' */
+        savepc(ci);
         if (TESTARG_k(i)) {
           int nparams1 = GETARG_C(i);
           if (nparams1)  /* vararg function? */
             ci->func -= ci->u.l.nextraargs + nparams1;
           luaF_close(L, base, LUA_OK);  /* there may be open upvalues */
         }
-        halfProtect(luaD_poscall(L, ci, n));
+        luaD_poscall(L, ci, n);
         return;
       }
       vmcase(OP_RETURN0) {