patch 8.1.1928: popup windows don't move with the text when making changes

Problem:    Popup windows don't move with the text when making changes.
Solution:   Add the 'textprop" property to the popup window options, position
            the popup relative to a text property. (closes #4560)
            No tests yet.
diff --git a/src/window.c b/src/window.c
index 8da5ed0..0507cee 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2522,6 +2522,10 @@
 	out_flush();
 #endif
 
+#ifdef FEAT_TEXT_PROP
+    if (popup_win_closed(win) && !win_valid(win))
+	return FAIL;
+#endif
     win_close_buffer(win, free_buf ? DOBUF_UNLOAD : 0, TRUE);
 
     if (only_one_window() && win_valid(win) && win->w_buffer == NULL