Ensure correct error message when have error decrypting parameter and also have keys that convert

[amanda11]

When you have an action that takes two key/value pairs whereby:

1. One parameter is encrypted and the key/value isnt' set
2. Another parameter is of a type other than string, and key/value pair is set

When the error is reported for the parameter that can't be decrypted, on handling that error another exception is raised when it attempts to validate the parameter json in regard to the parameter in key/value store that needs to be converted. This means that the incorrect error message is reported.
See #5312 for an example case of when this occurs.

Closes #5312

[CLAassistant]

All committers have signed the CLA.

[amanda11]

@Kami Thanks for review comments, I've addressed them now - and in process, realised I had one of the UT wrong! Ready for re-review when you get a chance.

[winem]

LGTM!