applets/weather: Center badge when the icon is smaller

Note this is a very small optimization of a few horizontal pixels for corner cases, but should help to avoid invading the space of the applet on the left (or make it less likely)

Pinging @akselmo who found the issue to check whether it helps his case

I wouldn't want to discuss the other issues the badge overlay presents for this small icon sizes in this MR.

BEFORE
AFTER