Bug 1404176 - Remove aborted print preview browser before bailing out. r=mconley

This patch clears out set of print preview browsers before bailing out when
there is an error while putting the document into print preview mode.

MozReview-Commit-ID: 20cm4DCktQk

--HG--
extra : rebase_source : 9881245cc09ef50cadd1139b6a9c1b32e7847612

toolkit/components/printing/content/printUtils.js

@@ -602,6 +602,7 @@ var PrintUtils = {
       if (message.data.failed) {
         // Something went wrong while putting the document into print preview
         // mode. Bail out.
+        this._ppBrowsers.clear();
         this._listener.onEnter();
         this._listener.onExit();
         return;