fix of TypeError: Cannot read property '0' of undefined

if array items are defined in schema and key is missing
f.e.:
schema:
{
	"type":"object",
	"$schema": "http://json-schema.org/draft-03/schema",
	"id": "http://jsonschema.net",
	"required":false,
	"properties":{
		"i": {
			"type":"array",
			"id": "http://jsonschema.net/i",
			"required":false,
			"items":[
				{
					"type":"object",
					"id": "http://jsonschema.net/i/0",
					"required":false,
					"properties":{
						"1": {
							"type":"number",
							"id": "http://jsonschema.net/i/0/1",
							"required":false
						}
					}
				},
				{
					"type":"object",
					"id": "http://jsonschema.net/i/1",
					"required":false,
					"properties":{
						"3": {
							"type":"number",
							"id": "http://jsonschema.net/i/1/3",
							"required":false
						}
					}
				}
			]
		}
	}
}


------------------------------

data:
{
  "i_key_is_missing": []
}