Description of the Issue

Floating side windows doesn't minimize to system tray.

Steps to Reproduce the Issue

1. Start Notepad++
2. Check Settings -> Preferences -> MISC. -> Minimize to system tray
3. Start Project Panel 1 and make it a floating window (Rip it out of it's docked position)
4. Click the minimize icon of Notepad++

Expected Behavior

Notepad++ and all floating windows belonging to it disappear, like they do on "normal" minimize.

Actual Behavior

Notepad++ disappears, the floating windows remain visible.

Debug Information

Notepad++ v7.9   (32-bit)
Build time : Sep 22 2020 - 03:24:22
Path : C:\Tools\Npp\notepad++.exe
Admin mode : OFF
Local Conf mode : ON
OS Name : Windows 10 Pro (64-bit) 
OS Version : 1607
OS Build : 14393.576
Current ANSI codepage : 1252
Plugins : DSpellCheck.dll LuaScript.dll mimeTools.dll NppConverter.dll NppExport.dll