src/rsvg-port.c: Correct usage of `FT_Bool` vs `gboolean` comparison.

`TRUE` in this context is from glib headers (`glib-2.0/glib/gmacros.h`),
imported indirectly from rsvg headers.  It should not be used for comparison
with `FT_Bool` types.  Other usages of `TRUE/FALSE` in this file is okay.

Signed-off-by: Hin-Tak Leung <htl10@users.sourceforge.net>