Empty commits cause build failures

## Orb version:
1.0.0

## What happened:

When using a path-filtering configuration without a single `continue_config.yml` file an empty commit (e.g. `git commit --allow-empty -m "[deploy-test] test deploy"`) causes a build failure. The build fails with the following message:

```
Checking For yq + CURL
Config list ===
.circleci/continue_config.yml
Generated YAML ===
Error: open .circleci/continue_config.yml: no such file or directory

Exited with code exit status 123
```

Sample circleci config which can be used to recreate the issue along with an empty commit:

```yaml
---
version: 2.1

setup: true

orbs:
path-filtering: circleci/path-filtering@1.0.0

workflows:
generate-config:
jobs:
- path-filtering/filter:
base-revision: << pipeline.git.branch >>
mapping: |
be/.* build-be true be/.circleci/config.yml
fe/.* build-fe true fe/.circleci/config.yml
.* build-root true .circleci/root_level_config.yml

```

## Expected behavior:

The build should not fail. Ideally, any catch-all path filtering configs (e.g. `.*`) should also run.

Start with the sample CircleCI setup configuration and reproduce the failure using an empty commit with no single continue_config.yml file. Trace the path-filtering/filter job's generated configuration and handling of the catch-all mapping; done means the build succeeds and catch-all path filters run as expected.

Written by the indexing model from the issue text.