patch 8.2.2947: build failure without the channel feature

Problem:    Build failure without the channel feature.
Solution:   Add back #ifdef. (John Marriott)
diff --git a/src/version.c b/src/version.c
index efb1b42..7bc2afc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2947,
+/**/
     2946,
 /**/
     2945,