patch 8.0.0341: undo does not work properly when using completion

Problem:    When using complete() and typing a character undo is saved after
            the character was inserted. (Shougo)
Solution:   Save for undo before inserting the character.
diff --git a/src/edit.c b/src/edit.c
index a37261f..d7f89bc 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -3583,7 +3583,11 @@
 {
 #ifdef FEAT_MBYTE
     int		cc;
+#endif
 
+    if (stop_arrow() == FAIL)
+	return;
+#ifdef FEAT_MBYTE
     if (has_mbyte && (cc = (*mb_char2len)(c)) > 1)
     {
 	char_u	buf[MB_MAXBYTES + 1];