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 #9306)
diff --git a/src/quickfix.c b/src/quickfix.c
index 1e25edb..c7abc8e 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -6793,13 +6793,18 @@
 
 /*
  * 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(qf_info_T *qi, dict_T *retdict)
 {
-    return dict_add_number(retdict, "qfbufnr",
-					(qi == NULL) ? 0 : qi->qf_bufnr);
+    int	bufnum = 0;
+
+    if (qi != NULL && buflist_findnr(qi->qf_bufnr) != NULL)
+	bufnum = qi->qf_bufnr;
+
+    return dict_add_number(retdict, "qfbufnr", bufnum);
 }
 
 /*
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index b242ac5..940b4d6 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -4626,6 +4626,13 @@
   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
diff --git a/src/version.c b/src/version.c
index 0864655..a8f2b36 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3762,
+/**/
     3761,
 /**/
     3760,