patch 8.0.0274: possible recursive screen updating causes trouble

Problem:    When update_single_line() is called recursively, or another screen
            update happens while it is busy, errors may occur.
Solution:   Check and update updating_screen. (Christian Brabandt)
diff --git a/src/version.c b/src/version.c
index a60de4c..5814b20 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    274,
+/**/
     273,
 /**/
     272,