patch 8.2.3408: can delete a numbered function

Problem:    Can delete a numbered function. (Naohiro Ono)
Solution:   Disallow deleting a numbered function. (closes #8760)

src/testdir/test_user_func.vim

@@ -434,6 +434,11 @@ func Test_del_func()
   func d.fn()
     return 1
   endfunc
+
+  " cannot delete the dict function by number
+  let nr = substitute(execute('echo d'), '.*function(''\(\d\+\)'').*', '\1', '')
+  call assert_fails('delfunction g:' .. nr, 'E475: Invalid argument: g:')
+
   delfunc d.fn
   call assert_equal({'a' : 10}, d)
 endfunc

src/userfunc.c

@@ -4669,6 +4669,13 @@ ex_delfunction(exarg_T *eap)
     if (eap->nextcmd != NULL)
 	*p = NUL;
 
+    if (isdigit(*name) && fudi.fd_dict == NULL)
+    {
+	if (!eap->skip)
+	    semsg(_(e_invarg2), eap->arg);
+	vim_free(name);
+	return;
+    }
     if (!eap->skip)
 	fp = find_func(name, is_global, NULL);
     vim_free(name);

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3408,
 /**/
     3407,
 /**/