patch 8.1.1431: popup window listed as "Scratch"

Problem:    Popup window listed as "Scratch".
Solution:   List them as "Popup".
diff --git a/src/buffer.c b/src/buffer.c
index ea61c5a..3bfb639 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5782,6 +5782,10 @@
 	if (bt_prompt(buf))
 	    return (char_u *)_("[Prompt]");
 #endif
+#ifdef FEAT_TEXT_PROP
+	if (bt_popup(buf))
+	    return (char_u *)_("[Popup]");
+#endif
 	return (char_u *)_("[Scratch]");
     }