fix(libkernel): return EFAULT from sceKernelStat and sceKernelUnlink for a null path - #7108

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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.