another fix for downloading error message

aqt/downloader.py

@@ -59,10 +59,11 @@ class Downloader(QThread):
             resp, cont = con.request(
                 aqt.appShared + "download/%d" % self.code)
         except Exception, e:
+            exc = traceback.format_exc()
             try:
                 self.error = unicode(e[0], "utf8", "ignore")
             except:
-                self.error = traceback.format_exc()
+                self.error = exc
             return
         finally:
             remHook("httpRecv", recvEvent)