patch 8.2.1557: crash in :vimgrep when started as "vim -n"

Problem:    Crash in :vimgrep when started as "vim -n". (Raul Segura)
Solution:   Check mfp pointer. (Yegappan Lakshmanan, closes #6827)
diff --git a/src/version.c b/src/version.c
index 022c90a..214ee2a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1557,
+/**/
     1556,
 /**/
     1555,