patch 8.0.0247: need to type Ctrl-N twice to select a completion

Problem:    Under some circumstances, one needs to type Ctrl-N or Ctrl-P twice
            to have a menu entry selected. (Lifepillar)
Solution:   call ins_compl_free(). (Christian Brabandt, closes #1411)
diff --git a/src/edit.c b/src/edit.c
index af1d00b..47932c9 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -2821,6 +2821,7 @@
     if (ctrl_x_mode != 0)
 	ins_compl_prep(' ');
     ins_compl_clear();
+    ins_compl_free();
 
     compl_direction = FORWARD;
     if (startcol > curwin->w_cursor.col)