cxl/mbox: Break poison list loop on an empty payload

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/cxl/core/mbox.c"
                    ],
                    "versions": [
                        {
                            "version": "ed83f7ca398b3798b82c1d5d1113011c0e5a2198",
                            "lessThan": "86771c105293ca26bfcc320b4f60d32c137b54aa",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "ed83f7ca398b3798b82c1d5d1113011c0e5a2198",
                            "lessThan": "42eab80981f4d2ac820e253e80ecf92f8cd91f69",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "ed83f7ca398b3798b82c1d5d1113011c0e5a2198",
                            "lessThan": "6ad491cef1a812cf7b53aa769cd8869516c47362",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "ed83f7ca398b3798b82c1d5d1113011c0e5a2198",
                            "lessThan": "e77594e0cea67ab1c2317a27aa77a744e26ad6a6",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "ed83f7ca398b3798b82c1d5d1113011c0e5a2198",
                            "lessThan": "8b301c4afbce4bc3f94528441d8d5ce1366504ad",
                            "status": "affected",
                            "versionType": "git"
                        }
                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "drivers/cxl/core/mbox.c"
                    ],
                    "versions": [
                        {
                            "version": "6.4",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "6.4",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.157",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12.110",
                            "lessThanOrEqual": "6.12.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.52",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.6",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }