This is a change from the default behavior in macdrv for as long as it's existed, as far as I can tell. Previously, gaining a dock icon was a one-way path. However, that doesn't jive with the way taskbar entries work on Windows; if an app has no windows, it doesn't appear in the taskbar. This patch attempts to remedy cases where an app winds up with superfluous dock icons for exe's that no longer have windows (looking at you, basically every launcher and Steam).
The major concern I can see with this is that if an app closes all of its windows but does not exit, there will be no indication that it is still running. Two thoughts on that:
1. That *should* be an anomalous case, such as the app hanging on exit. 2. Effectively the same behavior would happen on Windows.
I would love to hear any other thoughts about this change. I'm open (though I would not prefer it) to defaulting the registry key to false if that would alleviate any concerns.
-- v4: winemac.drv: Hide app's dock icon when it wouldn't have a taskbar item on Windows.