vim-patch:8.2.4416: Vim9: using a script-local function requires using "s:" (#29950)

Problem:    Vim9: using a script-local function requires using "s:" when
            setting 'completefunc'.
Solution:   Do not require "s:" in Vim9 script. (closes vim/vim#9796)

1fca5f3e86

vim-patch:8.2.4417: using NULL pointer

Problem:    Using NULL pointer.
Solution:   Set offset after checking for NULL pointer.

e89bfd212b

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

src/nvim/eval/userfunc.c

@@ -2084,7 +2084,7 @@ char *get_scriptlocal_funcname(char *funcname)
 
   if (strncmp(funcname, "s:", 2) != 0
       && strncmp(funcname, "<SID>", 5) != 0) {
-    // The function name is not a script-local function name
+    // The function name does not have a script-local prefix.
     return NULL;
   }