[BUG] cpp-qt5-client using --model-name-prefix option prevents generation of 'client.pri'

[dtucker61]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• [NA ] Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

Using the '--model-name-prefix ' command line option causes the 'client.pri' file to NOT be generated.
Related/Aside: using the '-c <file>' with file contents == { "optionalProjectFile":"true" } appears to have no effect.

openapi-generator version

4.0.0-beta
4.0.0-beta2

OpenAPI declaration file content or url

This issue appears to be independent of OpenAPI declaration file content.

Command line used for generation

The following generates a 'client.pri' file:
java -jar ${SWCG_JAR}/swagger-codegen.jar generate --enable-post-process-file --input-spec $1 --generator-name cpp-qt5-client --template-dir /space/data/Repositories/MustacheFiles/ForQtClient --output $4 -c $3

The following does not generate a 'client.pri' file:
java -jar ${SWCG_JAR}/swagger-codegen.jar generate --enable-post-process-file --input-spec $1 --generator-name cpp-qt5-client --template-dir /space/data/Repositories/MustacheFiles/ForQtClient --output $4 --model-name-prefix=$2 -c $3

Steps to reproduce

1. Issue the first CLI listed above.
2. Observe presence of 'client.pri' in the output directory.
3. Issue the second CLI command listed above.
4. Observe that the file 'client.pri' is not generated in the output directory.

Related issues/PRs

Case #730 appears to demonstrate a completely different syntax for using --model-name-prefix. Not sure if this is at all related.

Suggest a fix