Bug: Circular field dependency results in maximum call stack

This code:
```js
import {
	Schema,
	Query,
	ObjectType,
	Field,
	schemaFactory
} from 'graphql-schema-decorator'

@ObjectType()
class QueryType {
	@Field()
	other(): QueryType {
		return null
	}
}

@Schema()
class SchemaType {
	@Query() query: QueryType
}

schemaFactory(SchemaType)
```

Results in:
```
RangeError: Maximum call stack size exceeded
```