gdk-pixbuf/gdk-pixbuf-io.c: fix build without gmodule
gdk-pixbuf/gdk-pixbuf-io.c: fix build without gmodule

Fix the following build failure:

../gdk-pixbuf/gdk-pixbuf-io.c: In function 'gdk_pixbuf_io_init':
../gdk-pixbuf/gdk-pixbuf-io.c:681:16: error: implicit declaration of function 'gdk_pixbuf_get_module_file'; did you mean '_gdk_pixbuf_get_module'? [-Werror=implicit-function-declaration]
  681 |  module_file = gdk_pixbuf_get_module_file ();
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~
      |                _gdk_pixbuf_get_module

Fixes:
 - http://autobuild.buildroot.org/results/6cd54c497f5d19342ec94ece713547b887e4c02d

Signed-off-by: Fabrice Fontaine <7d88633730b8b85c1516e612893df72eae9cd341@gmail.com>

GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf