nsdoc files once loaded do not show descriptions

[danyill]

Describe the bug

When nsdoc files are loaded the user should see nice descriptions in, for instance the IED editor

To Reproduce
Steps to reproduce the behavior:

1. Open SCD file, here's an example: test_file.scd.zip
2. Load nsdocs under Settings
3. Open IED editor
4. See no descriptions

Expected behavior

Want descriptions!

Screenshots

When I open the sample file, I see no descriptions with the nsdocs loaded:

Additional context

It seems like the functions called in getDataDescription are referring to null objects:

open-scd/packages/openscd/src/foundation/nsdoc.ts

Lines 3 to 74 in 9c5859e

	export interface Nsdoc {
	nsdoc72?: XMLDocument;
	nsdoc73?: XMLDocument;
	nsdoc74?: XMLDocument;
	nsdoc81?: XMLDocument;
	getDataDescription: (element: Element, ancestors?: Element[]) => { label: string; }
	}
	const [nsd72, nsd73, nsd74, nsd81] = await Promise.all([iec6185072, iec6185073, iec6185074, iec6185081]);
	/**
	* Initialize the full Nsdoc object.
	* @returns A fully initialized Nsdoc object for wizards/editors to use.
	*/
	export function initializeNsdoc(): Nsdoc {
	const [nsdoc72, nsdoc73, nsdoc74, nsdoc81] = [
	localStorage.getItem('IEC 61850-7-2') ? new DOMParser().parseFromString(localStorage.getItem('IEC 61850-7-2')!, 'application/xml') : undefined,
	localStorage.getItem('IEC 61850-7-3') ? new DOMParser().parseFromString(localStorage.getItem('IEC 61850-7-3')!, 'application/xml') : undefined,
	localStorage.getItem('IEC 61850-7-4') ? new DOMParser().parseFromString(localStorage.getItem('IEC 61850-7-4')!, 'application/xml') : undefined,
	localStorage.getItem('IEC 61850-8-1') ? new DOMParser().parseFromString(localStorage.getItem('IEC 61850-8-1')!, 'application/xml') : undefined
	]
	const iedElementTagNames = ['LN', 'LN0', 'DO', 'SDO', 'DOI', 'DA', 'BDA', 'DAI'] as const;
	type IEDElementTagNames = typeof iedElementTagNames[number];
	type GetDataDescription = (element: Element, ancestors?: Element[]) => { label: string; };
	const getDataDescriptions: Record<
	IEDElementTagNames,
	{
	getDataDescription: GetDataDescription;
	}
	> = {
	LN: {
	getDataDescription: getLNDataDescription
	},
	LN0: {
	getDataDescription: getLNDataDescription
	},
	DO: {
	getDataDescription: getDODataDescription
	},
	SDO: {
	getDataDescription: getSDODataDescription
	},
	DOI: {
	getDataDescription: getDODataDescription
	},
	DA: {
	getDataDescription: getDADataDescription
	},
	BDA: {
	getDataDescription: getBDADataDescription
	},
	DAI: {
	getDataDescription: getDADataDescription
	}
	};
	/**
	* Getting data descriptions for LN(0) elements out of the IEC 61850-7-4 .nsdoc file.
	* @param element - The element to use for searching the LN description.
	* @returns Documentation from the .nsdoc file for this LN(0) file, or the lnClass attribute in case no description can be found.
	*/
	function getLNDataDescription(element: Element): { label: string; } {
	const lnClassAttribute = element.getAttribute('lnClass')!;
	const lnClass = nsd74.querySelector(`NS > LNClasses > LNClass[name="${lnClassAttribute}"]`);
	const lnClassDescription = getNsdocDocumentation(nsdoc74!, lnClass?.getAttribute('titleID'));
	return {
	label: lnClassDescription ? lnClassDescription + ' (' + lnClassAttribute + ')' : lnClassAttribute
	};
	}

e.g.

function getLNDataDescription(element: Element): { label: string; } { 
     const lnClassAttribute = element.getAttribute('lnClass')!; 
     const lnClass = nsd74.querySelector(`NS > LNClasses > LNClass[name="${lnClassAttribute}"]`); 
     const lnClassDescription = getNsdocDocumentation(nsdoc74!, lnClass?.getAttribute('titleID')); 
  
     return { 
       label: lnClassDescription ? lnClassDescription + ' (' + lnClassAttribute + ')' : lnClassAttribute 
     }; 
   } 

On my machine, very often, for instance nsdoc74 is null.
In this file it's hard for me to see how it can be anything other than null as it is defined in initializeNsdoc within the function scope and it is not available in the getXXDataDescription functions.

PR with a possible fix coming shortly.