Reference to external files fails

Description

All references to parameters in another file fail if any one reference to another file fails.

I have a yaml file where I have given references to parameters in another files. If one of the references fails due to a file missing then all the references present in the file present after that point in the file fail to work.

Swagger-codegen version

Code gen-Version : 3.0.21

Swagger declaration file content or url

For example I have below file swagger.yaml in which I give reference to another files responses.yaml and common.yaml

swagger. yaml

paths:
 /pets:
    get:
        responses:
               '400':
                   $ref: 'responses.yaml#/components/responses/400'
               '401': 
                   $ref:  'common.yaml#/components/responses/401'

Now if responses.yaml file is missing then the reference to common.yaml will also not work even though common.yaml is present.

Command line used for generation

java -jar swagger-codegen-cli-3.0.21.jar -i swagger.yaml -l html

Reproduce the issue with swagger.yaml, responses.yaml, and common.yaml using the documented swagger-codegen-cli-3.0.21 command and the html generator. Compare behavior when responses.yaml is missing; done means the valid reference to common.yaml still resolves instead of being skipped after the missing reference.