fix: guard disconnectedCallback against undefined aplayer and prevent duplicate initialization (#105)

- Add null check for this.aplayer in disconnectedCallback to prevent
  'Cannot read properties of undefined (reading destroy)' error when
  the element is moved in the DOM before the async fetch completes
- Add _initialized flag to prevent connectedCallback from running
  _init() and _parse() multiple times when the element is re-inserted
  into the DOM (e.g., by jQuery DOM manipulation libraries)
- Reset _initialized on proper disconnect so the element can be reused

Fixes #66

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: METO <metowolf@users.noreply.github.com>

Author: metowolf

src/Meting.js

@@ -1,15 +1,17 @@
 class MetingJSElement extends HTMLElement {
 
   connectedCallback() {
-    if (window.APlayer && window.fetch) {
+    if (window.APlayer && window.fetch && !this._initialized) {
+      this._initialized = true
       this._init()
       this._parse()
     }
   }
 
   disconnectedCallback() {
-    if (!this.lock) {
+    if (!this.lock && this.aplayer) {
       this.aplayer.destroy()
+      this._initialized = false
     }
   }