Re: `font-face-attributes' sometimes returns bogus :height value

[Chong Yidong]

>>> If `font-face-attributes' is called without a specified height, it
>>> returns an attribute list containing `:height nil', which is invalid.
>>
>>> Since it is quite useful to work with no specified, I think this case
>>> should be supported properly.
>>
>>> To make this work means either omitting the :height attribute entirely
>>> from the returned attribute-list, or alternatively, keeping it, but
>>> using `:height unspecified' for the height.
>>
>> I think :weight thru :width should also be omitted or
>> `unspecified' in the above case.

Done.