patch 8.2.2473: crash when leaving command line window triggers autocommand

Problem:    Crash when leaving command line window triggers autocommand.
            (houyunsong)
Solution:   Make sure not to close the current window or buffer.

Author: brammool

src/ex_getln.c

@@ -4403,12 +4403,12 @@ open_cmdwin(void)
 
 	// win_goto() may trigger an autocommand that already closes the
 	// cmdline window.
-	if (win_valid(wp))
+	if (win_valid(wp) && wp != curwin)
 	    win_close(wp, TRUE);
 
 	// win_close() may have already wiped the buffer when 'bh' is
-	// set to 'wipe'
-	if (bufref_valid(&bufref))
+	// set to 'wipe', autocommands may have closed other windows
+	if (bufref_valid(&bufref) && bufref.br_buf != curbuf)
 	    close_buffer(NULL, bufref.br_buf, DOBUF_WIPE, FALSE, FALSE);
 
 	// Restore window sizes.

src/testdir/test_autocmd.vim

@@ -2774,4 +2774,13 @@ func Test_autocmd_normal_mess()
   augroup END
 endfunc
 
+func Test_autocmd_closing_cmdwin()
+  au BufWinLeave * nested q
+  call assert_fails("norm 7q?\n", 'E855:')
+
+  au! BufWinLeave
+  new
+  only
+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 */
+/**/
+    2473,
 /**/
     2472,
 /**/