[REG 5.14] Renderer process crash: Received bad user message: GamepadMonitor::GamepadStartPolling failed

Since Qt 5.14, when visiting a page using the HTML5 Gamepad feature, the renderer process often crashes with:

[89241:89255:1231/181844.488236:ERROR:render_process_host_impl.cc(4622)] Terminating render process for bad Mojo message: Received bad user message: GamepadMonitor::GamepadStartPolling faile
[89241:89255:1231/181844.488274:ERROR:bad_message.cc(27)] Terminating renderer for bad IPC message, reason 123

This also means it's impossible to use Jellyfin with a QtWebEngine-based browser, as it seems to use the Gamepad API on its login page.

To reproduce, visit https://html5gamepad.com/ in simplebrowser - if it doesn't crash right away, hit reload a couple of times. Here, it crashes around every 5th time, but on other pages it seems to be 100% reproducible.