fix: only issue getlegendgraphic requests for wms layers

[Grammostola]

Aims to fix #1884

[tonnyandersson]

Why not do like below instead of that lonely if statement?

} else {
  content = getTitleWithIcon(title, '');
}

Also, these changes make the changes in PR #1882 a bit redundant. Maybe the whole else if block on lines 244-245 can be removed since those situations will be covered by these changes? Or...?

EDIT 1: Ok, maybe not remove that whole block since there's actually a reason for the else if (!layer.get('type'))... to be there.

EDIT 2: Ok, maybe remove it after all, and add (layer.get('type') &&... to the subsequent else if statements. Makes more sense since the else if (!layer.get('type'))... statement's only purpose is to prevent the execution of the subsequent else if statements and not because typeless layers inherently need special treatment.

EDIT 3: I'm rambling.

[Grammostola]

I see what you are seeing, the block is a bit of an eyesore.

Something like this might work.. I'll check it on monday.

  const title = layer.get('title') || 'Titel saknas';
  let content = '';

  const style = viewer.getStyle(layer.get('styleName'));
  if (style && style[0] && (!style[0][0].extendedLegend)) {
    content = getStyleContent(title, style);
  } else {
    content = getTitleWithIcon(title, '');
    const lType = layer.get('type');
    if (lType && lType.includes('WMS')) {
      content = await getWMSJSONContent(title);
    } else if ((lType && lType.includes('AGS')) || /\/arcgis\/services\/[^/]+\/[^/]+\/MapServer\/WMSServer/.test(getOneUrl(layer))) {
      content = await getAGSJSONContent(title, layer.get('id'));
    }
  }