Fixed crash when typedesc[T] was the first param of a proc.

Very simple first bug fix :) Tested with:

````Nimrod
# foo.nim
type Bar* = object
  b*: int

type Baz* = object
  b*: string

proc new*(T:typedesc[Bar], b:int): Bar =
  result.b = b

proc new*(T:typedesc[Baz], b:string): Baz =
  result.b = b
````

````Nimrod
import foo

var br = Bar.new(120)
var bz = Baz.new("hello")

echo br.b
echo bz.b
````