patch 8.2.2474: using freed memory when window is closed by autocommand

Problem:    Using freed memory when window is closed by autocommand.
            (houyunsong)
Solution:   Check the window pointer is still valid.

src/quickfix.c

@@ -2603,6 +2603,8 @@ qflist_valid(win_T *wp, int_u qf_id)
 
     if (wp != NULL)
     {
+	if (!win_valid(wp))
+	    return FALSE;
 	qi = GET_LOC_LIST(wp);	    // Location list
 	if (qi == NULL)
 	    return FALSE;

src/testdir/test_autocmd.vim

@@ -2783,4 +2783,18 @@ func Test_autocmd_closing_cmdwin()
   only
 endfunc
 
+func Test_autocmd_vimgrep()
+  augroup aucmd_vimgrep
+    au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * sb
+    au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * q9
+  augroup END
+  " TODO: if this is executed directly valgrind reports errors
+  call assert_fails('lv?a?', 'E926:')
+
+  augroup aucmd_vimgrep
+    au!
+  augroup END
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2474,
 /**/
     2473,
 /**/