Move input validation from init to updateView

[Philschke]

📌 Overview

In addition to my recently raised issue #75,
I investigated the root cause and resolved it. This PR improves the control lifecycle by ensuring that input validation is performed in updateView instead of init.

❓ Why

According to Microsoft’s PCF guidelines:

Dataset and parameter values are not guaranteed to be initialized in init. Use updateView instead.

Running validation in init could therefore result in:

• Invalid states
• False errors
• Unpredictable behavior during initialization

🔧 Changes Made

• Removed checkInput call from init
• Moved validation logic to updateView, where parameters are guaranteed to be populated
• Kept init focused only on DOM setup and event handler registration
• Only check the input if it´s actually changed

🎯 Benefits

• Aligns control behavior with official PCF lifecycle best practices
• Prevents race conditions and incorrect error states during initialization