Fix Mac Qt port UI Crashes

I have already ported Flash4Linux ( https://github.com/netpipe/Flash4Linux ) to Qt 5.12. On macOS, however, the program still crashes whenever I hover over the timeline widget. My priority is simple: bring the interface back to the responsiveness of the original so I can focus on creating Flash animations instead of fighting crashes.

You’ll need to:
• Reproduce and isolate the macOS-only crash (most symptoms appear while hovering or dragging on the timeline).
• Patch the underlying C++/Qt 5.12 code so the UI never segfaults or freezes and remains just as responsive as before.
• Submit your changes as a clean pull request to the GitHub repository.

Acceptance criteria
1. Application starts and runs on macOS without asserts or segmentation faults.
2. All other features, old Flash file compatibility included, remain intact.