patch 9.0.1934: :bwipe fails after switching window from aucmd_win.

Problem:  :bwipe fails after switching window from aucmd_win.
Solution: Decrement b_nwindows after switching back to aucmd_win.

closes: #13160

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>

src/autocmd.c

@@ -1635,7 +1635,6 @@ aucmd_restbuf(
     {
 	win_T *awp = aucmd_win[aco->use_aucmd_win_idx].auc_win;
 
-	--curbuf->b_nwindows;
 	// Find "awp", it can't be closed, but it may be in another tab
 	// page. Do not trigger autocommands here.
 	block_autocmds();
@@ -1656,8 +1655,8 @@ aucmd_restbuf(
 	    }
 	}
 win_found:
+	--curbuf->b_nwindows;
 #ifdef FEAT_JOB_CHANNEL
-	;
 	int save_stop_insert_mode = stop_insert_mode;
 	// May need to stop Insert mode if we were in a prompt buffer.
 	leaving_window(curwin);

src/testdir/test_autocmd.vim

@@ -3630,11 +3630,22 @@ func Test_closing_autocmd_window()
   END
   call v9.CheckScriptFailure(lines, 'E814:')
   au! BufEnter
-  only!
   bwipe Xa.txt
   bwipe Xb.txt
 endfunc
 
+func Test_switch_window_in_autocmd_window()
+  edit Xa.txt
+  tabnew Xb.txt
+  autocmd BufEnter Xa.txt wincmd w
+  doautoall BufEnter
+  au! BufEnter
+  bwipe Xa.txt
+  call assert_false(bufexists('Xa.txt'))
+  bwipe Xb.txt
+  call assert_false(bufexists('Xb.txt'))
+endfunc
+
 func Test_bufwipeout_changes_window()
   " This should not crash, but we don't have any expectations about what
   " happens, changing window in BufWipeout has unpredictable results.

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1934,
 /**/
     1933,
 /**/