fix(libkernel): reject empty mkdir paths

core/libs/prx/libkernel/File/src/Stdio.cpp

@@ -544,6 +544,7 @@ int APS5_VABI getdents_nid_postfix(int fd, char* buf, int nbytes) {
 int APS5_VABI sceKernelMkdir(const char* path, uint16_t mode) {
     (void)mode;
     if (path == nullptr) throw std::invalid_argument("sceKernelMkdir: path is null");
+    if (!*path) return SceErrorFromErrno(GUEST_ENOENT);
     auto native = ResolvePath_nid_no_patch(path);
     while (!native.has_filename() && native.has_relative_path()) native = native.parent_path();
     std::error_code error;

core/libs/tests/GuestKernelSync.cpp

@@ -37,6 +37,7 @@ static bool Recorded(const char* guest) {
 }
 int main() {
     std::filesystem::remove_all("kernel_sync_probe");
+    Require(sceKernelMkdir("", 0777) == static_cast<int>(0x80020002u));
     Require(sceKernelMkdir("/", 0777) == static_cast<int>(0x80020011u));
     Require(sceKernelMkdir("kernel_sync_probe", 0777) == 0);
     Require(Recorded("kernel_sync_probe"));