fix own property lookup for primitive values

[drsm]

>> Object.getOwnPropertyDescriptor(1, 'toFixed')
{
 value: [Function: native],
 writable: true,
 enumerable: false,
 configurable: true
}
>> 1..hasOwnProperty('toFixed')
true

test262: built-ins/Symbol/prototype/description/is-not-own-property.js