Fix beastify code (#505)

* Fix blank page bug when clicking popup background

beastify/popup/choose_beast.js

@@ -65,6 +65,10 @@ function listenForClicks() {
      * Get the active tab,
      * then call "beastify()" or "reset()" as appropriate.
      */
+    if (e.target.tagName !== "BUTTON" || !e.target.closest("#popup-content")) {
+      // Ignore when click is not on a button within <div id="popup-content">.
+      return;
+    } 
     if (e.target.type === "reset") {
       browser.tabs.query({active: true, currentWindow: true})
         .then(reset)