Fix TypeError on round(self.humidity) (fixes #13116)

[mvn23]

During init, some (most?) platforms postpone the first update for a while. This produces errors in the log as home assistant is trying to round() uninitialised variables. This commit fixes that

Description:

fixes #13116

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox.

[homeassistant]

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[OttoWinter]

Nice 👍 Just a quick comment about falsy values.

[OttoWinter]

The if self.humidity check will not work with falsy values like 0.0.

Write something like if self.humidity is not None or, even better, make it an additional check like the other attributes:

data = {
            ATTR_WEATHER_TEMPERATURE: show_temp(
                self.hass, self.temperature, self.temperature_unit,
                self.precision),
        }

        humidity = self.humidity
        if humidity is not None:
            data[ATTR_WEATHER_HUMIDITY] = humidity

[mvn23]

You are absolutely right, hadn't thought about that.
Even though humidity is probably never going to be 0, we should definitely take it into account.
Fixed in the commit below.