patch 8.1.0016: possible crash in term_wait()

Problem:    Possible crash in term_wait(). (Dominique Pelle)
Solution:   Check for a valid buffer after ui_delay(). (closes #2944)
diff --git a/src/terminal.c b/src/terminal.c
index 817e6b9..6967df7 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -5264,11 +5264,11 @@
 	{
 	    mch_check_messages();
 	    parse_queued_messages();
+	    ui_delay(10L, FALSE);
 	    if (!buf_valid(buf))
 		/* If the terminal is closed when the channel is closed the
 		 * buffer disappears. */
 		break;
-	    ui_delay(10L, FALSE);
 	}
 	mch_check_messages();
 	parse_queued_messages();