Adds a null check to label templates, adds return types for validation methods

[Godmartinz]

This adds a null check on the validation of the template for labels and a return type for the validation methods.

adds a notification if template is null:

This checks if the template selection is not null in the db at save and while trying to render the label preview

[what-the-diff]

PR Summary

• Introduction of Return Type Declarations
  Several methods (validate, validateUnits, validateSize, validateMargins, and validateSupport) in Label.php have been improved by defining their return type as void. This means these methods will not return any value, making the program more predictable and easier to debug.

• Improved Error Handling Mechanism
  Error handling has been enhanced in the render method of Label.php. If the $template variable is null, it now throws an exception. This enhancement provides a robust method to catch and deal with potential errors in code execution, helping to maintain the stability of the application.

[marcusmoore]

Quick question

[marcusmoore]

Couple (hopefully) quick things

[marcusmoore]

Looks good 👍🏾