applets/weather: Fix system tray detection

The applet needs to check weather it is in the system tray to avoid showing a text label beside the icon.

As the property is a flag, it needs a bitwise operator instead of a plain equality. This also adds a second check (in practice both are true, but better safe than sorry)

Additionally, also hide the option completely instead of showing it disabled, which can be confusing.

BEFORE	AFTER