Use the right FcConfig for FcFontList

Passing NULL for a config argument in a fontconfig
api means we are using the default configuration,
which may be different from the one the fontmap
is supposed to be using.

Fix an instance of this in pango_fc_face_list_sizes.
5 jobs for fix-FcConfig-uses in 5 minutes and 47 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Build
passed linux-fedora #1170542

00:00:51

passed macos #1170544
macos

00:05:44

passed msys2-mingw64 #1170543
win32-ps

00:01:40

 
  Analysis
passed asan-build #1170545
asan

00:01:40

 
  Docs
passed reference #1170546

00:00:57