[Fontconfig] test ft-font-create-for-ft-face fails

[Patrick Lam]

sunmoon1997 wrote:
> hi,
>   while running testsuit in cairo, the test ft-font-create-for-ft-face
> failed with a pretty crash. After a quick look, the problem is
> FcPatternAddString in fontconfig 2.4 branch doesn't accept null string
> any more. The fix should be trivial, but I don't know the fix should go
> cairo or fontconfig, so I attached both of them for review.

The fix should go into fontconfig.  I've committed a slightly modified
patch that preserves the old behaviour of FcPatternAddString; I
inadvertently changed the behaviour on null strings at some point.

pat