parser: reorder alias expansion routine to return early

I think it improves readability to move trivial cases first, and unindent
blocks.

mercurial/parser.py

@@ -509,31 +509,29 b' class basealiasrules(object):'
         if not isinstance(tree, tuple):
             return tree
         a = cls._getalias(aliases, tree)
-        if a is not None:
+        if a is None:
+            return tuple(cls._expand(aliases, t, expanding, cache)
+                         for t in tree)
             if a.error:
                 raise error.Abort(a.error)
             if a in expanding:
                 raise error.ParseError(_('infinite expansion of %(section)s '
                                          '"%(name)s" detected')
-                                       % {'section': cls._section,
-                                          'name': a.name})
+                                   % {'section': cls._section, 'name': a.name})
             expanding.append(a)
             if a.name not in cache:
                 cache[a.name] = cls._expand(aliases, a.replacement, expanding,
                                             cache)
             result = cache[a.name]
             expanding.pop()
-            if a.args is not None:
+        if a.args is None:
+            return result
                 l = cls._getlist(tree[2])
                 if len(l) != len(a.args):
                     raise error.ParseError(_('invalid number of arguments: %d')
                                            % len(l))
                 l = [cls._expand(aliases, t, [], cache) for t in l]
-                result = cls._expandargs(result, dict(zip(a.args, l)))
-        else:
-            result = tuple(cls._expand(aliases, t, expanding, cache)
-                           for t in tree)
-        return result
+        return cls._expandargs(result, dict(zip(a.args, l)))
 
     @classmethod
     def expand(cls, aliases, tree):