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": []
}