patch 8.1.0466: autocmd test fails

Problem:    Autocmd test fails.
Solution:   Do call inchar() when flushing typeahead.
diff --git a/src/memline.c b/src/memline.c
index f7a3d06..0881e6c 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -4522,7 +4522,7 @@
 
 			// If vimrc has "simalt ~x" we don't want it to
 			// interfere with the prompt here.
-			flush_buffers(TRUE);
+			flush_buffers(FLUSH_TYPEAHEAD);
 		    }
 
 #if defined(FEAT_GUI_DIALOG) || defined(FEAT_CON_DIALOG)