patch 9.0.0301: the message window popup is delayed after an error message

Problem:    The message window popup is delayed after an error message.
Solution:   Do not set emsg_on_display when using the message window.
diff --git a/src/message.c b/src/message.c
index aa3506e..e73b837 100644
--- a/src/message.c
+++ b/src/message.c
@@ -750,8 +750,12 @@
 #endif
     }
 
-    emsg_on_display = TRUE;	// remember there is an error message
-    attr = HL_ATTR(HLF_E);	// set highlight mode for error messages
+#ifdef HAS_MESSAGE_WINDOW
+    if (!use_message_window())
+#endif
+	emsg_on_display = TRUE;	    // remember there is an error message
+
+    attr = HL_ATTR(HLF_E);	    // set highlight mode for error messages
     if (msg_scrolled != 0)
 	need_wait_return = TRUE;    // needed in case emsg() is called after
 				    // wait_return has reset need_wait_return