Bug in donation banner prevents display

I'm sorry to report the donation banner did not display when it was supposed to, at 2017-10-23T00:00:00. I tracked down the problem to a line in the code that was used for testing:

if (Services.prefs.getBoolPref("extensions.torbutton.testBanner", false)) {

Unfortunately, this line throws an exception if the pref does not exist at all. (The exception causes the banner not to be shown, while no other code is affected.) The second argument to getBoolPref is documented as the "default value" in mozilla-central, but not in mozilla-esr52. It seems I read the mozilla-central documentation, not realizing the second argument was added in Firefox 54.

And further, while I tested the banner with the pref set to true and false, it's clear I didn't test the banner thoroughly enough with the pref deleted.

I apologize for this mistake, especially to Georg and Nicolas who already ran extra builds for the banner.