patch 8.0.1403: using freed buffer in grep command

Problem:    Using freed buffer in grep command. (gy741, Dominique Pelle)
Solution:   Lock the dummy buffer to avoid autocommands wiping it out.

src/quickfix.c

@@ -4572,6 +4572,7 @@ load_dummy_buffer(
     bufref_T	newbuf_to_wipe;
     int		failed = TRUE;
     aco_save_T	aco;
+    int		readfile_result;
 
     /* Allocate a buffer without putting it in the buffer list. */
     newbuf = buflist_new(NULL, NULL, (linenr_T)1, BLN_DUMMY);
@@ -4585,6 +4586,9 @@ load_dummy_buffer(
     /* need to open the memfile before putting the buffer in a window */
     if (ml_open(newbuf) == OK)
     {
+	/* Make sure this buffer isn't wiped out by auto commands. */
+	++newbuf->b_locked;
+
 	/* set curwin/curbuf to buf and save a few things */
 	aucmd_prepbuf(&aco, newbuf);
 
@@ -4599,9 +4603,11 @@ load_dummy_buffer(
 	curbuf->b_flags &= ~BF_DUMMY;
 
 	newbuf_to_wipe.br_buf = NULL;
-	if (readfile(fname, NULL,
+	readfile_result = readfile(fname, NULL,
 		    (linenr_T)0, (linenr_T)0, (linenr_T)MAXLNUM,
-		    NULL, READ_NEW | READ_DUMMY) == OK
+		    NULL, READ_NEW | READ_DUMMY);
+	--newbuf->b_locked;
+	if (readfile_result == OK
 		&& !got_int
 		&& !(curbuf->b_flags & BF_NEW))
 	{

src/testdir/test_autocmd.vim

@@ -1171,3 +1171,10 @@ func Test_nocatch_wipe_all_buffers()
   bwipe
   au!
 endfunc
+
+func Test_nocatch_wipe_dummy_buffer()
+  " Nasty autocommand: wipe buffer on any event.
+  au * x bwipe
+  call assert_fails('lv½ /x', 'E480')
+  au!
+endfunc

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1403,
 /**/
     1402,
 /**/