Seeing error from quickfolders-util.js:1461:15 - can't access property "disabled", doc.getElementById(...) is null

[WoofGrrrr]

Debugging my own extensions and saw this. Thought you might want to know...

12:10:08.089 Quickfolders.Interface.initCurrentFolderTab()
can't access property "disabled", doc.getElementById(...) is null
 aSourceName: chrome://quickfolders/content/quickfolders-interface.js, line: 7109, copl: 0, flg: 1 disableNavigation
  chrome://quickfolders/content/quickfolders-interface.js:7109:11
initCurrentFolderTab@chrome://quickfolders/content/quickfolders-interface.js:7164:26
liftNavigationbar@chrome://quickfolders/content/quickfolders-interface.js:1371:9
injectCurrentFolderBar/<@jar:file:///C:/Users/markb/AppData/Roaming/Thunderbird/Profiles/4x4rl22v.default-release/extensions/quickfolders@curious.be.xpi!/chrome/content/scripts/qf-3pane.js:266:32
quickfolders-util.js:1461:15

[RealRaven2000]

Although these buttons should exist if the navigation bar (current folder toolbar) exists, so initCurrentFolderTab() should effectively early exit before it comes to this place, I added some code that guards against missing buttons here:

QuickFolders-mx-6.14.2pre9.zip