Fix Sending Wrong Values on Failed Conversion to DPT

[cornelius-koepp]

Issue

Setting a value which cannot be converted to the given DPT did result in unexpected behaviour.

• valueNoSendCompare/valueCompare resulted in value 0 (and returned change based on this value)
• valueNoSend updated state from unitialized to OK, without updating the value
• value wrote to GA without setting the KO value

Reproduce

For all cases use a value/type combination which results in KNX_Encode_Value return false.

Example: value 500 with type DPT_Value_1_Ucount, or any other

Note: DPT1 will not fail; ignoring all other bits.

• valueNoSendCompare/valueCompare: did always set value to 0 (no special preconditions needed beside conversion fail)
• valueNoSend: use before any other change of KO. No change in value expected, but read requests will answered (with undefined value)
• value use before any other change of KO. Will result in write telegram (with other value included)

Fix

Suppress updating, status-update and sending for invalid values.

To Discuss

The fix does not change the public interface for changing/writing KO values, so there will be no feedback if conversion fails. Current methods return type void could be changed to bool to indicate success, without breaking.

[Ing-Dom]

please add a short description in the Changelog about this
then I will merge it
https://github.com/OpenKNX/knx/blob/v1dev/README.md#v1dev-replace-this-with-version-and-date-when-releasing-to-v1