patch 8.2.4168: disallowing empty function name breaks existing plugins

Problem:    Disallowing empty function name breaks existing plugins.
Solution:   Allow empty function name in legacy script.
diff --git a/src/testdir/sautest/autoload/foo.vim b/src/testdir/sautest/autoload/foo.vim
index 298e727..21d33a0 100644
--- a/src/testdir/sautest/autoload/foo.vim
+++ b/src/testdir/sautest/autoload/foo.vim
@@ -9,3 +9,7 @@
 func foo#addFoo(head)
   return a:head .. 'foo'
 endfunc
+
+func foo#()
+  return 'empty'
+endfunc
diff --git a/src/testdir/test_autoload.vim b/src/testdir/test_autoload.vim
index 384ee1a..21de655 100644
--- a/src/testdir/test_autoload.vim
+++ b/src/testdir/test_autoload.vim
@@ -10,6 +10,9 @@
   call assert_equal(1, g:called_foo_bar_echo)
 
   eval 'bar'->g:foo#addFoo()->assert_equal('barfoo')
+
+  " empty name works in legacy script
+  call assert_equal('empty', foo#())
 endfunc
 
 func Test_source_autoload()
@@ -23,4 +26,5 @@
   call assert_equal(49, auto9#add42(7))
 endfunc
 
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/userfunc.c b/src/userfunc.c
index 5de5dd0..223535f 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3693,8 +3693,8 @@
     // Note that TFN_ flags use the same values as GLV_ flags.
     end = get_lval(start, NULL, &lv, FALSE, skip, flags | GLV_READ_ONLY,
 					      lead > 2 ? 0 : FNE_CHECK_START);
-    if (end == start
-		   || (end != NULL && end[-1] == AUTOLOAD_CHAR && *end == '('))
+    if (end == start || (in_vim9script() && end != NULL
+				   && end[-1] == AUTOLOAD_CHAR && *end == '('))
     {
 	if (!skip)
 	    emsg(_(e_function_name_required));
diff --git a/src/version.c b/src/version.c
index 27ee162..cea8ece 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4168,
+/**/
     4167,
 /**/
     4166,