Fix for MQTT subscription validation loop

[ra1u]

Issue is that validation can accept invalid elements, because it does not interrupt loop on failure.
Proposed patch improves this.

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[AniruddhaKanhere]

Thank you @ra1u for taking the time to report this issue.

I have one minor suggestion. Let us know if you'd like us to make the change on your behalf (we'd need permission to collaborate on your fork).

Thanks

[ra1u]

Thank you Aniruddha Kanhere

I noticed I made merge bug when accepting suggested change over web.
Regarding permission, fell free to change. Let me know if I need to click on some permission button.

Kind regards!