vim-patch:8.2.3762: if quickfix buffer is wiped out getqflist() still returns it

Problem:    If the quickfix buffer is wiped out getqflist() still returns its
            number.
Solution:   Use zero if the buffer is no longer present. (Yegappan Lakshmanan,
            closes vim/vim#9306)
56150da687

src/nvim/quickfix.c

@@ -6020,12 +6020,18 @@ static int qf_winid(qf_info_T *qi)
 }
 
 /// Returns the number of the buffer displayed in the quickfix/location list
-/// window. If there is no buffer associated with the list, then returns 0.
+/// window. If there is no buffer associated with the list or the buffer is
+/// wiped out, then returns 0.
 static int qf_getprop_qfbufnr(const qf_info_T *qi, dict_T *retdict)
   FUNC_ATTR_NONNULL_ARG(2)
 {
-  return tv_dict_add_nr(retdict, S_LEN("qfbufnr"),
+  int bufnum = 0;
-                        (qi == NULL) ? 0 : qi->qf_bufnr);
+
+  if (qi != NULL && buflist_findnr(qi->qf_bufnr) != NULL) {
+    bufnum = qi->qf_bufnr;
+  }
+
+  return tv_dict_add_nr(retdict, S_LEN("qfbufnr"), bufnum);
 }
 
 /// Convert the keys in 'what' to quickfix list property flags.

src/nvim/testdir/test_quickfix.vim

@@ -4483,6 +4483,13 @@ func Xqfbuf_test(cchar)
   call assert_equal(qfbnum, bufnr(''))
   Xclose
 
+  " When quickfix buffer is wiped out, getqflist() should return 0
+  %bw!
+  Xexpr ""
+  Xopen
+  bw!
+  call assert_equal(0, g:Xgetlist({'qfbufnr': 0}).qfbufnr)
+
   if a:cchar == 'l'
     %bwipe
     " For a location list, when both the file window and the location list