Fix ArgumentException when FontName in setting file is not valid

[AndisGrossteins]

Fixes #468

The check for invalid font name and falling back to default font might be better placed in LogExpert.Config.ConfigManager but I've added it in LogWindow where the exception was thrown blocking application startup.

[Hirogen]

why not implement it in the configmanager? if it would be the right place?

[AndisGrossteins]

why not implement it in the configmanager? if it would be the right place?

I wasn't sure how to approach it better. Now moved it into ConfigManager.

[Copilot]

Pull Request Overview

This PR fixes an ArgumentException that occurs when the FontName specified in the configuration file is invalid, which was blocking application startup. The fix adds validation during configuration loading to detect invalid font names and fall back to the default monospace font.

Key Changes:

• Added font name validation in the configuration loading process
• Implemented fallback mechanism to default monospace font when validation fails
• Added logging to inform users when font fallback occurs

[Copilot]

The FontFamily instance is created but only used to validate the font name and get its canonical name. Consider disposing of the FontFamily instance or use a more efficient validation approach to avoid potential resource leaks.

Suggested change

	var fontFamily = new FontFamily(settings.Preferences.FontName);
	settings.Preferences.FontName = fontFamily.Name;
	using (var fontFamily = new FontFamily(settings.Preferences.FontName))
	{
	settings.Preferences.FontName = fontFamily.Name;
	}

[Copilot]

FontFamily.GenericMonospace.Name is accessed multiple times (here and on line 215). Consider storing it in a variable to avoid repeated property access.

Suggested change

	_logger.Warn($"Specified font '{settings.Preferences.FontName}' not found. Falling back to default: '{FontFamily.GenericMonospace.Name}'. {ex.Message}");
	settings.Preferences.FontName = FontFamily.GenericMonospace.Name;
	var genericMonospaceName = FontFamily.GenericMonospace.Name;
	_logger.Warn($"Specified font '{settings.Preferences.FontName}' not found. Falling back to default: '{genericMonospaceName}'. {ex.Message}");
	settings.Preferences.FontName = genericMonospaceName;

[Hirogen]

No need to log the exception in the warning

[AndisGrossteins]

I agree. I'll add using to dispose of the FontFamily instance as suggested by Copilot.

[Hirogen]

i'm a little nit picky here, but you can remove the "ex" variable, because we don't use it anyway :)

[AndisGrossteins]

Ah, right. Let me just remove it, then.