Strip name of added deck

There is currently what I believe to be a bug: create a deck "   ".
The creation is accepted and the name is renamed to "blank". Instead,
I believe you'd want to strip the deck name before testing its
emptiness.

qt/aqt/studydeck.py

@@ -145,6 +145,7 @@ class StudyDeck(QDialog):
         else:
             default = self.names[self.form.list.currentRow()]
         n = getOnlyText(_("New deck name:"), default=default)
+        n = n.strip()
         if n:
             did = self.mw.col.decks.id(n)
             # deck name may not be the same as user input. ex: ", ::