jscript: Use jsstr_flatten to access string buffer in dispex.c.

dlls/jscript/dispex.c

@@ -1524,8 +1524,15 @@ HRESULT disp_delete_name(script_ctx_t *ctx, IDispatch *disp, jsstr_t *name, BOOL
     jsdisp = iface_to_jsdisp((IUnknown*)disp);
     if(jsdisp) {
         dispex_prop_t *prop;
+        const WCHAR *ptr;
+
+        ptr = jsstr_flatten(name);
+        if(!ptr) {
+            jsdisp_release(jsdisp);
+            return E_OUTOFMEMORY;
+        }
 
-        hres = find_prop_name(jsdisp, string_hash(name->str), name->str, &prop);
+        hres = find_prop_name(jsdisp, string_hash(ptr), ptr, &prop);
         if(prop) {
             hres = delete_prop(prop, ret);
         }else {