Fix opentherm_gw climate TypeError in current_temperature if no temperature is known.

[mvn23]

Description:

Fix TypeError in the opentherm_gw climate platform in case the library doesn't report a temperature value. Initialize _current_temperature and _target_temperature to None instead of 0.0.

Related issue (if applicable): fixes #21695

Pull request in home-assistant.io with documentation (if applicable): N/A

Example entry for configuration.yaml (if applicable):

N/A

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If user exposed functionality or configuration variables are added/changed:

• N/A

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New or updated dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• N/A

[gnkarn]

this may be the same case with other sensors too (?), for example i receive this message :

Invalid state ( > 263): [<class 'decimal.ConversionSyntax'>]
10:07 components/utility_meter/sensor.py (WARNING) - message first occured at 10:07 and shows up 2 times

when this sensor fails to report its meassure ,

utility_meter:
  daily_energy:
    source: sensor.home_energy_sensor_aparent
    cycle: daily 
  monthly_energy:
    source: sensor.home_energy_sensor_aparent
    cycle: monthly

and the sensor itself is

- platform: mqtt
  name: "Home Energy sensor_aparent"
  state_topic: "ESPURNA_energy/data"
  value_template: "{{ value_json.apparent }}"
  unit_of_measurement: "W"

  qos: 1
- platform: mqtt
  name: "Home Energy sensor_energy"
  state_topic: "ESPURNA_energy/data"
  value_template: "{{ value_json.energy }} "
  unit_of_measurement: "J"
  qos: 1
- platform: mqtt
  name: "Home Energy sensor_rssi"
  state_topic: "ESPURNA_energy/data"
  value_template: "{{ (value_json.rssi) | round(1) }} "
  unit_of_measurement: "db"
  qos: 1
  

  
- platform: template
  sensors:
    home_energy_kwh:
      unit_of_measurement: 'Kwh'
      value_template: >-
              {{ (states('sensor.home_energy_sensor_energy') | float / 3600000) | round(3) }}
- platform: template
  sensors:
    home_energy_cost:
      friendly_name: "Home Energy cost"
      entity_id: sensor.home_energy_kwh
      unit_of_measurement: "$"
      value_template: >-
        {{ states('sensor.home_energy_kwh')  | multiply(6) | round(2) }}              

[MartinHjelmare]

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