patch 8.2.3337: completing "call g:" returns entries with just "g:"

Problem:    Completing "call g:" returns entries with just "g:". (Naohiro Ono)
Solution:   Skip empty strings returned by get_user_func_name(). (closes #8753)
diff --git a/src/version.c b/src/version.c
index a31b494..64137db 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3337,
+/**/
     3336,
 /**/
     3335,