app: [Windows] use the app ID for the window class registry

We're about to send messages between multiple instances of the same
program, and we need something to distinguish Gio programs. Use the
app ID.

Signed-off-by: inkeliz <inkeliz@inkeliz.com>
Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_windows.go

@@ -132,13 +132,19 @@ func initResources() error {
 	}
 	resources.cursor = c
 	icon, _ := windows.LoadImage(hInst, iconID, windows.IMAGE_ICON, 0, 0, windows.LR_DEFAULTSIZE|windows.LR_SHARED)
+
+	appid, err := syscall.UTF16PtrFromString(ID)
+	if err != nil {
+		return err
+	}
+
 	wcls := windows.WndClassEx{
 		CbSize:        uint32(unsafe.Sizeof(windows.WndClassEx{})),
 		Style:         windows.CS_HREDRAW | windows.CS_VREDRAW | windows.CS_OWNDC,
 		LpfnWndProc:   syscall.NewCallback(windowProc),
 		HInstance:     hInst,
 		HIcon:         icon,
-		LpszClassName: syscall.StringToUTF16Ptr("GioWindow"),
+		LpszClassName: appid,
 	}
 	cls, err := windows.RegisterClassEx(&wcls)
 	if err != nil {