Keep empty brace of companion object

[yukukotani]

Fixes #411

keep empty brace of companion object from removing, because the removing causes compile error.

Current

class test {
    // Unnecessary block ("{}")
    companion object {}
    enum class ExampleEnum {
        EXAMPLE
    }
}

// Formatted
class test {
    companion object
    enum class ExampleEnum {
        // Compile error
        EXAMPLE
    }
}

Patched

class test {
    // No error
    companion object {}
    enum class ExampleEnum {
        EXAMPLE
    }
}

[Tapchicoma]

Thank you for fixing this!