Overlapping attributes in inherited types fails to convert

Hi! Thanks for creating this tool, it's been a life saviour for us for generating OpenAPI definitions. We want to have a single source of truth for our type definitions, so a tool like this comes pretty handy.

However, I found an issue when type converting interfaces that inherit from other interfaces that share common attributes.

Let's imagine we have the following declarations:
```TypeScript
interface Base {
$type: string;
comment: string;
}

interface A {
$type: 'a';
a: string;
}

export interface Foo extends Base, A {
$type: 'a';
}
```

The conversion works as expected. However, if `interface A` has declared an attribute that matches one in the `Base` interface, the CLI gives an error `Cannot read properties of undefined (reading 'length')`. With a bit of testing I was able to narrow the issue down to the changes version `2.3.0`. Previous versions have no issues with converting this, though, looking at the release notes it's supposedly because they weren't being converted at all 😄

Here's a modified example of the one above that reproduces the error:
```TypeScript
interface Base {
$type: string;
comment: string;
}

interface A {
$type: 'a';
a: string;
comment: string;
}

export interface Foo extends Base, A {
$type: 'a';
}
```

Consideration for debugging: it would be nice to be able to see where the errors are generated from. The error didn't output any information regarding file or line number in regards to what was producing it. My project has quite extensive types that are converted using `typeconv`, so it took a while to find what was causing the error.