FcConfigParseAndLoad*() should returns false on config errors

Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/168

Reported by Lawrence D'Oliveiro
diff --git a/src/fcxml.c b/src/fcxml.c
index 2e5898e..1591c5a 100644
--- a/src/fcxml.c
+++ b/src/fcxml.c
@@ -3620,7 +3620,7 @@
 	    FcConfigMessage (0, FcSevereError, "Cannot %s default config file", load ? "load" : "scan");
 	return FcFalse;
     }
-    return FcTrue;
+    return ret;
 }
 
 FcBool