patch 8.1.0064: typing CTRL-W in a prompt buffer shows mode "-- --"

Problem:    Typing CTRL-W in a prompt buffer shows mode "-- --".
Solution:   Set restart_edit to 'A' and check for it.
diff --git a/src/window.c b/src/window.c
index 4f4f08b..f059b37 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2114,6 +2114,8 @@
     // When leaving a prompt window stop Insert mode and perhaps restart
     // it when entering that window again.
     win->w_buffer->b_prompt_insert = restart_edit;
+    if (restart_edit != 0 && mode_displayed)
+	clear_cmdline = TRUE;		/* unshow mode later */
     restart_edit = NUL;
 
     // When leaving the window (or closing the window) was done from a