emulators/virtualbox-ose{,-additions}{,-nox11}-legacy: Fix vboxvfs bugs

This commit fixes vboxvfs (shared foler) kernel module bugs:

• fix open file leaks on creating files that causes file descriptor leaks on host;
• fix halfway lookups.

PR: 245865
MFH: 2025Q1
(cherry picked from commit abe3df235ee4885d7937f2626f566ea48715e02c)