fixed "empty array"-bug

This fixes a bug with valid empty JSON arrays.

Example: 

This JSON
{"cars":[]}

violates this schema
{
    "description": "cars",
    "type": "object",
    "properties": {
        "cars": {
            "type": "array",
            "required": true,
            "minItems": 0,
            "items": [
                {
                    "type": "object",
                    "required": true,
                    "properties": {
                        "carBrand": {
                            "type": "string",
                            "required": true
                        },
                        "carModel": {
                            "type": "string",
                            "required": true
}}}]}}}

with this error
cars[0] - is missing and it is required