fix no element error

tools/chromium_extension/js/content-script.js

@@ -2,30 +2,32 @@
 
     let URLObj = new URL(location.href)
     console.log(URLObj)
+    if( document.querySelector("#readme table tbody")) {
 
-    let audio_player = new Audio()
-    audio_player.setAttribute('autoplay', 'true')
-    document.querySelector("#readme table tbody").addEventListener('click', (event) => {
-        console.log(event)
-        console.log(event.target.nodeType)
-        console.log(event.target.nodeName)
-        event.preventDefault();
-        event.stopPropagation();
+        let audio_player = new Audio()
+        audio_player.setAttribute('autoplay', 'true')
+        document.querySelector("#readme table tbody").addEventListener('click', (event) => {
+            console.log(event)
+            console.log(event.target.nodeType)
+            console.log(event.target.nodeName)
+            event.preventDefault();
+            event.stopPropagation();
 
-        let audio_url = null;
-        if (event.target.nodeName === 'TD') {
-            let aTag = event.target.querySelector('a');
-            if (aTag) {
+            let audio_url = null;
+            if (event.target.nodeName === 'TD') {
+                let aTag = event.target.querySelector('a');
+                if (aTag) {
+                    audio_url = aTag.getAttribute('href');
+                }
+            }
+            if (event.target.nodeName === 'IMG') {
+                let aTag = event.target.parentNode.parentNode
                 audio_url = aTag.getAttribute('href');
             }
-        }
-        if (event.target.nodeName === 'IMG') {
-            let aTag = event.target.parentNode.parentNode
-            audio_url = aTag.getAttribute('href');
-        }
-        if (audio_url) {
-            console.log("audio_url:", audio_url)
-            audio_player.setAttribute('src', audio_url);
-        }
-    })
+            if (audio_url) {
+                console.log("audio_url:", audio_url)
+                audio_player.setAttribute('src', audio_url);
+            }
+        })
+    }
 }