Fix segfault caused by cross-thread QProcess read in vpnLogger

[devnix]

Disclaimer: While I can read C/C++ to a certain extent, I've fully worked on fixing this issue with AI. I don't want, by any means, to pollute repositories with slop.

If I should make changes, I would love to have the opportunity to learn more from a review. Thank you for your patience! 🙏🏼

Summary

• Root cause: vpnLogger runs in a dedicated QThread but was calling QProcess::read() on a QProcess owned by the main thread via a QSignalMapper queued connection. This caused QRingBuffer corruption and frequent segfaults, especially under heavy VPN I/O (large downloads).
• Fix: Read QProcess data in its owning thread using a DirectConnection lambda on readyReadStandardOutput, then queue the already-read QByteArray to the logger thread via QMetaObject::invokeMethod for processing.
• Additional fixes in vpnProcess:
  • Add null checks for thread_worker and ptr_tunnel in onObserverUpdate(), updateStats(), and onStatsUpdate() timer callbacks.
  • Stop observer timers before thread cleanup in closeProcess() to prevent use-after-free.
  • Initialize timer pointers to nullptr in the constructor.
• Cleanup: Remove unused logMapperStdout, dead logVPNOutput slot, unused loglocker map, and add proper cleanup of per-VPN maps in procFinished() to prevent resource leaks on reconnect.

Crash backtrace (before fix)

#0  __memmove_avx_unaligned_erms (libc.so.6)
#1  QRingBuffer::read (libQt5Core.so.5)
#2  QIODevicePrivate::read (libQt5Core.so.5)
#3  QIODevice::read (libQt5Core.so.5)
#4  vpnLogger::logVPNOutput (openfortigui)
#5  vpnLogger::qt_static_metacall (openfortigui)
#6  QSignalMapper::mapped (libQt5Core.so.5)

Test plan

• Verified crash is reproducible before fix
• Verified no crash after fix under sustained VPN usage with heavy downloads
• Clean shutdown (exit code 0) confirmed
• Compiles cleanly with CMake on Ubuntu 24.04 / Qt 5.15