patch 8.2.1781: writing to prompt buffer interferes with insert mode

Problem:    Writing to prompt buffer interferes with insert mode.
Solution:   Use win_enter() instead of just setting "curwin". (Ben Jackson,
            closes #7035)
diff --git a/src/autocmd.c b/src/autocmd.c
index d5c61ca..4c2b705 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -1533,7 +1533,7 @@
 	unblock_autocmds();
 
 	if (win_valid(aco->save_curwin))
-	    curwin = aco->save_curwin;
+	    win_enter(aco->save_curwin, TRUE);
 	else
 	    // Hmm, original window disappeared.  Just use the first one.
 	    curwin = firstwin;