patch 8.2.3748: giving an error for an empty sign argument breaks a plugin

Problem:    Giving an error for an empty sign argument breaks a plugin.
Solution:   Do not give an error.
diff --git a/src/version.c b/src/version.c
index e7b0b2e..17dfe98 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3748,
+/**/
     3747,
 /**/
     3746,