vim-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.

e6a4200ff4

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/eval/userfunc.c

@@ -1760,8 +1760,7 @@ char_u *trans_function_name(char **pp, bool skip, int flags, funcdict_T *fdp, pa
   // Note that TFN_ flags use the same values as GLV_ flags.
   end = (char_u *)get_lval((char *)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) {
     if (!skip) {
       emsg(_("E129: Function name required"));
     }

src/nvim/testdir/sautest/autoload/foo.vim

@@ -9,3 +9,7 @@ endfunc
 func foo#addFoo(head)
   return a:head .. 'foo'
 endfunc
+
+func foo#()
+  return 'empty'
+endfunc

src/nvim/testdir/test_autoload.vim

@@ -10,6 +10,9 @@ func Test_autoload_dict_func()
   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()
@@ -17,3 +20,6 @@ func Test_source_autoload()
   source sautest/autoload/sourced.vim
   call assert_equal(1, g:loaded_sourced_vim)
 endfunc
+
+
+" vim: shiftwidth=2 sts=2 expandtab