patch 8.2.3743: ":sign" can add a highlight group without a name

Problem:    ":sign" can add a highlight group without a name.
Solution:   Give an error if the group name is missing. (closes #9280)
diff --git a/src/version.c b/src/version.c
index 531642e..cd7a964 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3743,
+/**/
     3742,
 /**/
     3741,