message: fix parsing usepackage
diff: @@ -208,12 +208,19 @@ export class Command {
  updatePkg(file: string, nodes?: latexParser.Node[], content?: string) {
  if (nodes !== undefined) {
  nodes.forEach(node => {
  - if (latexParser.isCommand(node) && node.name === 'usepackage' && 'args' in node) {
  + if (latexParser.isCommand(node) && node.name === 'usepackage') {
  node.args.forEach(arg => {
  if (latexParser.isOptionalArg(arg)) {
  return
  }
  - (arg.content[0] as latexParser.TextString).content.split(',').forEach(pkg => {
  + for (const c of arg.content) {
  + if (!latexParser.isTextString(c)) {
  + continue
  + }
  + c.content.split(',').forEach(pkg => {
  + if (/^\s*$/.exec(pkg)) {
  + return
  + }
  const pkgs = this.extension.manager.cachedContent[file].element.package
  if (pkgs) {
  pkgs.push(pkg)
  @@ -221,6 +228,7 @@ export class Command {
  this.extension.manager.cachedContent[file].element.package = [pkg]
  }
  })
  + }
  })
  } else {
  if (latexParser.hasContentArray(node)) {
  