OpenAPI: A service with no path to openapi contracts is not generated

### I tried this:

When i have a service configured to be generated with OpenAPI generator which has no path to an openapi contract the service is not generated.

I have a service which only consumes OpenAPI and does not provide a Rest interface is not generated.
```
[
'@eventcatalog/generator-openapi',
{
domain: {id: 'MyDomain', name: 'My Domain', version: '0.0.0'},
saveParsedSpecFile: true,
parseChannels: true,
debug: true,
services: [
{
id: 'my-only-consuming-openapi-service',
consumers: [
{id: 'other-providing-service'}
]
},
}
]
```

### This happened:

The service is not generated with the following error during `npm run generate` :
```
Failed to parse OpenAPI file: undefined
TypeError: Cannot read properties of undefined (reading 'startsWith')
```

### I expected this:

I would expect the service always to be generated, even if it does not proivide and does not consume any openapi contract.
The existance of a service should not be dependent on a contract.

### Is there a workaround?

There's no workaroud

### Anything else?

_No response_

### EventCatalog Version

"@eventcatalog/core": "4.3.4", "@eventcatalog/generator-openapi": "9.0.0",

### Node.js Version

v22.22.0

### Platform(s)

Linux

### Community Notes

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Start by reproducing the issue with the shown generator-openapi configuration and npm run generate. Trace service generation when no OpenAPI contract path is provided, focusing on the undefined startsWith error. Done means the consuming-only service is generated successfully without an OpenAPI contract.

Written by the indexing model from the issue text.