patch 8.0.0673: build failure without conceal feature

Problem:    Build failure without conceal feature.
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index d15b7db..b9f309d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    673,
+/**/
     672,
 /**/
     671,