Merge PR mebjas#913 from upstream

Author: mokalovesoulmate

src/html5-qrcode-scanner.ts

@@ -1012,7 +1012,9 @@ export class Html5QrcodeScanner {
     public resetHeaderMessage() {
         const messageDiv = document.getElementById(
             this.getHeaderMessageContainerId())!;
-        messageDiv.style.display = "none";
+        if(messageDiv){
+            messageDiv.style.display = "none";
+        }
     }
 
     /*eslint complexity: ["error", 5]*/