Fix premature popup dismissal on Ubuntu & ChromeOS

Fix for [Issue #1](#1). Patch due to [Bao Ho](https://plus.google.com/102553037065128878831), who posted it to the [support pages] (post titled "_Solution for the problem of space switch in linux_").

Author: jmason888

js/background.js

@@ -74,6 +74,12 @@ var spaces = (function () {
     //add listeners for tab and window focus changes
     //when a tab or window is changed, close the move tab popup if it is open
     chrome.windows.onFocusChanged.addListener(function(windowId) {
+        // Prevent a click in the popup on Ubunto or ChroneOS from closing the
+        // popup prematurely.
+        if (windowId == chrome.windows.WINDOW_ID_NONE || windowId == spacesPopupWindowId) {
+            return;
+        }
+        
         if (!debug && spacesPopupWindowId) {
             if (spacesPopupWindowId) {
                 closePopupWindow();