Added invalid nickname error for conversations

[Jxpxn]

We currently cannot know if the input nickname is invalid (less than 1 character & more than 50 characters) and if the lib changed it to the default nickname ("Host").

[Jxpxn]

@Jxpxn please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.
• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

Contributor License Agreement

@microsoft-github-policy-service agree

[glharper]

@Jxpxn Thank you for this PR, I will build and test the changes, with the aim of including this in version 1.26.0 (due early spring)

[glharper]

Thanks again for this PR. :-)