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/evalfunc.c b/src/evalfunc.c
index b90c6d7..2b50798 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2304,7 +2304,7 @@
     if (intidx < 0)
     {
 	name = get_user_func_name(xp, idx);
-	if (name != NULL)
+	if (name != NULL && *name != NUL)
 	{
 	    if (*name != '<' && STRNCMP("g:", xp->xp_pattern, 2) == 0)
 		return cat_prefix_varname('g', name);
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 90afe45..3c5513b 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -657,6 +657,11 @@
   " g: prefix also works
   call feedkeys(":echo g:Test_cmdline_complete_user_f\<Tab>\<Home>\"\<cr>", 'tx')
   call assert_match('"echo g:Test_cmdline_complete_user_func', @:)
+
+  " using g: prefix does not result in just "g:" matches from a lambda
+  let Fx = { a ->  a }
+  call feedkeys(":echo g:\<Tab>\<Home>\"\<cr>", 'tx')
+  call assert_match('"echo g:[A-Z]', @:)
 endfunc
 
 func Test_cmdline_complete_user_names()
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,