RPM file scan failed

[aeg]

What happened:
If system has *.rpm files tha are not in rpm format, I will get an error at runtime and syft will not ouput SPDX file.

2022/09/27 17:16:16 error during command execution: 1 error occurred:
        * file is not an RPM

ls -l syft_spdx.json
-rw-r--r-- 1 root root 0  9月 28 13:46 syft_spdx.json

What you expected to happen:
Even if parsing the rpm file fails, syft continue processing and will output SPDX file.

How to reproduce it (as minimally and precisely as possible):

mkdir /tmp/aaa
echo "aaa" > /tmp/aaa/a.rpm
syft pakages dir:/tmp/aaa

Anything else we need to know?:
In some environments, simple ASCII files may exist even with the extension rpm, so please avoid errors even if they occur.
RPM file scanning support was added at v0.56.0 ,that affected.
I think syft can handle rpmutils errors.

A workaround is to add --exlucde **/*.rpm

Environment:

• Output of syft version:

syft version
Application:        syft
Version:            0.57.0
JsonSchemaVersion:  3.3.2
BuildDate:          2022-09-19T20:42:27Z
GitCommit:          04d288b3643f906255af88108f27712bb2be5b63
GitDescription:     v0.57.0
Platform:           linux/amd64
GoVersion:          go1.18.6
Compiler:           gc

• OS (e.g: cat /etc/os-release or similar):

NAME="Ubuntu"
VERSION="20.04.5 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.5 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal