fix(libkernel): return EFAULT from sceKernelStat and sceKernelUnlink for a null path

[pushkarreddyy]

What

sceKernelStat and sceKernelUnlink threw std::invalid_argument when passed a null path, terminating the calling title. In FreeBSD 11, sys_stat and sys_unlink return EFAULT (0x8002000e in PS5 errno) when the user path pointer cannot be copied from guest memory.

Both entry points now return 0x8002000e (SCE_KERNEL_ERROR_EFAULT) when path == nullptr instead of throwing.

Tested

Added unit tests in core/libs/tests/GuestPosixScalarIo.cpp (guest_posix_scalar_io) verifying that sceKernelStat and sceKernelUnlink with a null path fail with 0x8002000e without throwing.
python tools/check_conventions.py --base origin/main passed cleanly with zero findings.

Checklist

• Conventional Commit title
• Code follows the conventions in docs/dev/CONVENTIONS.md
• Technical debt recorded in docs/dev/TechnicalDebt.md
• Unit test added
• Depends on: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

[github-actions]

Some comparisons could not be completed because a pull request conflicts with the base branch. Review these shared files manually before concluding that there is no overlap.

Pull request	Shared files not compared
PR 5021	core/libs/prx/libkernel/File/src/Open.cpp
PR 6044	core/libs/tests/GuestPosixScalarIo.cpp

[pushkarreddyy]

Thank you @oneandonlydean for reviewing and merging #7103!

I have rebased #7108 directly onto latest origin/main (04788b090). As discussed on #7110 and #7113, once #7108 merges, I will immediately update #7110 with the folded changes (combining sceKernelTruncate, sceKernelUtimes, sceKernelMkdir, sceKernelRmdir, and sceKernelRename) and close #7113 and #7114.

Whenever you have a moment, please also check our other green PRs passing all CI checks:

• fix(libkernel): return EFAULT from sceKernelWriteThrottlingStatus for a null status #7133 (fix(libkernel): return EFAULT from sceKernelWriteThrottlingStatus for a null status) — fixes null status pointer fault on Minecraft Bedrock (PPSA17221, Minecraft Bedrock (PPSA17221) runs on Windows: boots to a playable world, 0 absent imports #5744).
• feat(libs): declare missing RUDP and signaling imports for PPSA31327 #7125 (feat(libs): declare missing RUDP and signaling imports for PPSA31327) — unblocks start-up for Yakuza 0 Director's Cut (PPSA31327, Yakuza 0 Director's Cut (PPSA31327) #6722).
• ci(relinker): run TLS function coverage tests under ASan on Linux #7096 (ci(relinker): run TLS function coverage tests under ASan on Linux) — addresses relinker CI: run TLS coverage tests under ASan so the #6401 overread can't return silently #7062.
• fix(libSceAgcDriver): normalize reserved bit 30 in guest buffer descriptors #7089 (fix(libSceAgcDriver): normalize reserved bit 30 in guest buffer descriptors) — addresses Code Violet (PPSA26528): abort at compute shader 0x147b9e400, "buffer descriptor has reserved bits set", new between d92a8dad3 and 51acb79ac #7051.