AutoMod: handle set_flair lists of < 2 items

A definition like `set_flair: ["flair text"]` will currently fail
without displaying an error, since set_flair can currently only handle
either lists of 2+ items or a single string (not inside a list). This
makes it so that a value of a list of < 2 strings will work correctly.

r2/r2/lib/automoderator.py

@@ -582,9 +582,14 @@ def set_values(self, values):
                 setattr(self, key, None)
 
         # special handling for set_flair
-        if self.set_flair:
+        if self.set_flair is not None:
             if isinstance(self.set_flair, basestring):
                 self.set_flair = [self.set_flair, ""]
+
+            # handle 0 or 1 item lists
+            while len(self.set_flair) < 2:
+                self.set_flair.append("")
+
             self.set_flair = {
                 "text": self.set_flair[0],
                 "class": self.set_flair[1],