[FIX] mail: fix compute of isMobileDevice

Follow up of https://github.com/odoo/odoo/commit/2c9da836e5829b8a3d3a36afbeebfdd78f36d542/#diff-f884c81b21062d0a63935bbdbc9c7cf52dc69a6a29ea4dce13130196435b0591R53

Value was permanently undefined: writing value on itself rather than from env.

closes odoo/odoo#89050

X-original-commit: 9dde44b1479118e55eb2e73df56e5e696c2bf850
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/static/src/models/device.js

@@ -31,7 +31,7 @@ registerModel({
                 globalWindowInnerHeight: this.messaging.browser.innerHeight,
                 globalWindowInnerWidth: this.messaging.browser.innerWidth,
                 isMobile: this.env.device.isMobile,
-                isMobileDevice: this.messaging.device.isMobileDevice,
+                isMobileDevice: this.env.device.isMobileDevice,
                 sizeClass: this.env.device.size_class,
             });
         },