bug (?) with nested templates in generic proc

[mratsim]

Here is a nice one:

This doesn't compile
    
    
    proc foo*(s:openarray): auto =
      discard
    # Error: invalid type: 'T' in this context: 'proc (s: openArray): untyped'
    
    
    Run

This compiles:
    
    
    proc foo*(s:openarray, N: static[int] = 0): auto =
      discard
    
    
    Run

see: <https://github.com/nim-lang/Nim/issues/6343>