patch 8.0.0634: cannot easily get to the last quickfix list

Problem:    Cannot easily get to the last quickfix list.
Solution:   Add "$" as a value for the "nr" argument of getqflist() and
            setqflist(). (Yegappan Lakshmanan)
diff --git a/src/quickfix.c b/src/quickfix.c
index b1a5ebd..8b61e10 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4670,7 +4670,14 @@
     {
 	qi = GET_LOC_LIST(wp);
 	if (qi == NULL)
+	{
+	    /* If querying for the size of the location list, return 0 */
+	    if (((di = dict_find(what, (char_u *)"nr", -1)) != NULL) &&
+		    (di->di_tv.v_type == VAR_STRING) &&
+		    (STRCMP(di->di_tv.vval.v_string, "$") == 0))
+		    return dict_add_nr_str(retdict, "nr", 0, NULL);
 	    return FAIL;
+	}
     }
 
     qf_idx = qi->qf_curlist;		/* default is the current list */
@@ -4685,6 +4692,18 @@
 		qf_idx = di->di_tv.vval.v_number - 1;
 		if (qf_idx < 0 || qf_idx >= qi->qf_listcount)
 		    return FAIL;
+	    } else if (qi->qf_listcount == 0)	    /* stack is empty */
+		return FAIL;
+	    flags |= QF_GETLIST_NR;
+	} else if ((di->di_tv.v_type == VAR_STRING) &&
+		(STRCMP(di->di_tv.vval.v_string, "$") == 0))
+	{
+	    {
+		/* Get the last quickfix list number */
+		if (qi->qf_listcount > 0)
+		    qf_idx = qi->qf_listcount - 1;
+		else
+		    qf_idx = -1;	/* Quickfix stack is empty */
 	    }
 	    flags |= QF_GETLIST_NR;
 	}
@@ -4692,17 +4711,20 @@
 	    return FAIL;
     }
 
-    if (dict_find(what, (char_u *)"all", -1) != NULL)
-	flags |= QF_GETLIST_ALL;
+    if (qf_idx != -1)
+    {
+	if (dict_find(what, (char_u *)"all", -1) != NULL)
+	    flags |= QF_GETLIST_ALL;
 
-    if (dict_find(what, (char_u *)"title", -1) != NULL)
-	flags |= QF_GETLIST_TITLE;
+	if (dict_find(what, (char_u *)"title", -1) != NULL)
+	    flags |= QF_GETLIST_TITLE;
 
-    if (dict_find(what, (char_u *)"winid", -1) != NULL)
-	flags |= QF_GETLIST_WINID;
+	if (dict_find(what, (char_u *)"winid", -1) != NULL)
+	    flags |= QF_GETLIST_WINID;
 
-    if (dict_find(what, (char_u *)"context", -1) != NULL)
-	flags |= QF_GETLIST_CONTEXT;
+	if (dict_find(what, (char_u *)"context", -1) != NULL)
+	    flags |= QF_GETLIST_CONTEXT;
+    }
 
     if (flags & QF_GETLIST_TITLE)
     {
@@ -4895,7 +4917,10 @@
 		qf_idx = di->di_tv.vval.v_number - 1;
 	    if (qf_idx < 0 || qf_idx >= qi->qf_listcount)
 		return FAIL;
-	}
+	} else if (di->di_tv.v_type == VAR_STRING &&
+		STRCMP(di->di_tv.vval.v_string, "$") == 0 &&
+		qi->qf_listcount > 0)
+	    qf_idx = qi->qf_listcount - 1;
 	else
 	    return FAIL;
 	newlist = FALSE;	/* use the specified list */
@@ -4923,6 +4948,7 @@
     if ((di = dict_find(what, (char_u *)"context", -1)) != NULL)
     {
 	typval_T	*ctx;
+
 	free_tv(qi->qf_lists[qf_idx].qf_ctx);
 	ctx =  alloc_tv();
 	if (ctx != NULL)