patch 9.0.0020: with some completion reading past end of string

Problem:    With some completion reading past end of string.
Solution:   Check the length of the string.
diff --git a/src/insexpand.c b/src/insexpand.c
index 4a5feac..734550f 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2209,11 +2209,21 @@
     // but only do this, if the Popup is still visible
     if (c == Ctrl_E)
     {
+	char_u *p = NULL;
+
 	ins_compl_delete();
 	if (compl_leader != NULL)
-	    ins_bytes(compl_leader + get_compl_len());
+	    p = compl_leader;
 	else if (compl_first_match != NULL)
-	    ins_bytes(compl_orig_text + get_compl_len());
+	    p = compl_orig_text;
+	if (p != NULL)
+	{
+	    int	    compl_len = get_compl_len();
+	    int	    len = (int)STRLEN(p);
+
+	    if (len > compl_len)
+		ins_bytes_len(p + compl_len, len - compl_len);
+	}
 	retval = TRUE;
     }