fix: resolve TS18048 type error

Author: zimya

lib/index.js

@@ -510,7 +510,10 @@ function startTag(node, state) {
   resetTokenizer(state, pointStart(node))
 
   const current = state.parser.openElements.current
-  let ns = 'namespaceURI' in current ? current.namespaceURI : webNamespaces.html
+  let ns =
+    current && 'namespaceURI' in current
+      ? current.namespaceURI
+      : webNamespaces.html
 
   if (ns === webNamespaces.html && tagName === 'svg') {
     ns = webNamespaces.svg
@@ -633,8 +636,8 @@ function documentMode(node) {
   const head = node.type === 'root' ? node.children[0] : node
   return Boolean(
     head &&
-      (head.type === 'doctype' ||
-        (head.type === 'element' && head.tagName.toLowerCase() === 'html'))
+    (head.type === 'doctype' ||
+      (head.type === 'element' && head.tagName.toLowerCase() === 'html'))
   )
 }