patch 8.2.2069: the quickfix window is not updated after setqflist()

Problem:    The quickfix window is not updated after setqflist().
Solution:   Update the quickfix buffer. (Yegappan Lakshmanan, closes #7390,
            closes #7385)
diff --git a/src/quickfix.c b/src/quickfix.c
index 5e46ad2..d7a163d 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -7349,7 +7349,7 @@
     if (action == 'r')
 	qf_free_items(&qi->qf_lists[qf_idx]);
     if (qf_init_ext(qi, qf_idx, NULL, NULL, &di->di_tv, errorformat,
-		FALSE, (linenr_T)0, (linenr_T)0, NULL, NULL) > 0)
+		FALSE, (linenr_T)0, (linenr_T)0, NULL, NULL) >= 0)
 	retval = OK;
 
     return retval;
@@ -7474,8 +7474,10 @@
     if ((di = dict_find(what, (char_u *)"quickfixtextfunc", -1)) != NULL)
 	retval = qf_setprop_qftf(qi, qfl, di);
 
-    if (retval == OK)
+    if (newlist || retval == OK)
 	qf_list_changed(qfl);
+    if (newlist)
+	qf_update_buffer(qi, NULL);
 
     return retval;
 }