applets/weather: Add missing null checks
Fixes the QML warnings when modelData
is undefined
ForecastView.qml:71: TypeError: Value is undefined and could not be converted to an object
ForecastView.qml:86: TypeError: Value is undefined and could not be converted to an object
ForecastView.qml:108: TypeError: Value is undefined and could not be converted to an object
Amends commit 79f77bda