Fix set-temperature controls in climate more-info for falsy temperatures

[thomasloven]

Fix #4296 (I assume. I haven't tested it because none of my climate devices go to 0 degrees...)

[oandrew]

I suspect this broke the UI for thermostats that can dynamically switch between one or two setpoints.

For instance, when thermostat is in single setpoint mode in has attributes:

temperature: 67
target_temp_high: null
target_temp_low: null

stateObj.attributes.target_temp_low !== undefined evalutes to true and makes all temperature controls visible.

I think it should be stateObj.attributes.target_temp_low != null instead.
Tricky javascript :)

[bramkragten]

Please create an issue for this, but it should probably check for both null and undefined