patch 8.1.1810: popup_getoptions() is missing an entry for "mapping"

Problem:    Popup_getoptions() is missing an entry for "mapping".
Solution:   Add the entry.
diff --git a/src/popupwin.c b/src/popupwin.c
index f2297f5..ca75181 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2319,6 +2319,7 @@
 	dict_add_string(dict, "title", wp->w_popup_title);
 	dict_add_number(dict, "wrap", wp->w_p_wrap);
 	dict_add_number(dict, "drag", (wp->w_popup_flags & POPF_DRAG) != 0);
+	dict_add_number(dict, "mapping", (wp->w_popup_flags & POPF_MAPPING) != 0);
 	dict_add_number(dict, "resize", (wp->w_popup_flags & POPF_RESIZE) != 0);
 	dict_add_number(dict, "cursorline",
 				   (wp->w_popup_flags & POPF_CURSORLINE) != 0);