Fix missing prefix on map types where value is an array of structs

[MiddleMan5]

Given converter with prefix = "test_" and exported types:

type MapArrayValue struct {
	Name string `json:"name"`
}
type StructWithEnumMapArrayStruct struct {
	Value  string                     `json:"value"`
	Values map[string][]MapArrayValue `json:"values"`
}

Output misses prefix on nested struct type

export interface test_StructWithEnumMapArrayStruct {
  value: string;
  values: {[key: string]: MapArrayValue[]};
}
export interface test_MapArrayValue {
  name: string;
}

This PR addresses this edge case and includes unit tests