Fix subscribe button when logged out

src/invidious/views/watch.ecr

@@ -155,7 +155,10 @@
 </div>
 
 <script>
-document.getElementById("subscribe")["href"] = "javascript:void(0);"
+subscribe_button = document.getElementById("subscribe");
+if (subscribe_button.getAttribute('onclick')) {
+    subscribe_button["href"] = "javascript:void(0);";
+}
 
 function subscribe() {
     var url = "/subscription_ajax?action_create_subscription_to_channel=1&c=<%= video.ucid %>&referer=<%= env.get("current_page") %>";