Animated emotes disappear after staying in an inactive window

[CaptainFlint]

Checklist

• [X] I'm reporting a problem with Chatterino
• [X] I've verified that I'm running the most recent nightly build or stable release
• [X] I've looked for my problem on the wiki
• [X] I've searched the issues and pull requests for similar looking reports

Describe your issue

When I keep Chatterino running in background for some time (about half an hour, maybe an hour), when I next time Alt+Tab into it, I see empty spaces instead of all the animated emotes. All the normal ones remain visible. This disappearance is not permanent; as soon as I hover mouse over amy of those empty places, all the emotes are redrawn again.

Conditions which seem to be required for reproducing the issue:

1. emote animations are turned off;
2. there are no new messages posted in chat during that period when I kept the Chatterino window inactive (in my case it was an offline channel).

If these conditions are not met, the issue doesn't seem to arise.

Two screenshots are attached: one is how the window normally look after posting a couple of test messages with emotes (one normal, two animated), and the second is how it looks after staying inactive for a while. (The screenshots have "2.4.0-beta" in the title, because it took a while to prepare the report, and there was no 2.4.0 final yet; but I've rechecked in the newly released 2.4.0, and it's the same there.)

This did not happen in 2.3.5; maybe because that version did not support animated emotes at all, and always showed only the first frame.

Screenshots

OS and Chatterino Version

Chatterino 2.4.0 (commit a0f93100 modified) built with Qt 5.15.2, Windows SDK, MSVC 193331631 Running on Windows 10 Version 2009, kernel: 10.0.19045