patch 9.0.1270: crash when using search stat in narrow screen

Problem:    Crash when using search stat in narrow screen.
Solution:   Check length of message. (closes #11921)
diff --git a/src/search.c b/src/search.c
index 9c8cf95..1e4464b 100644
--- a/src/search.c
+++ b/src/search.c
@@ -3154,7 +3154,11 @@
 	len += 2;
     }
 
-    mch_memmove(msgbuf + STRLEN(msgbuf) - len, t, len);
+    size_t msgbuf_len = STRLEN(msgbuf);
+    if (len > msgbuf_len)
+	len = msgbuf_len;
+    mch_memmove(msgbuf + msgbuf_len - len, t, len);
+
     if (dirc == '?' && stat.cur == maxcount + 1)
 	stat.cur = -1;