patch 8.1.1799: cannot avoid mapping for a popup window

Problem:    Cannot avoid mapping for a popup window.
Solution:   Add the "mapping" property, default TRUE.
diff --git a/src/getchar.c b/src/getchar.c
index fe1cc7e..4a3587c 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1575,6 +1575,9 @@
 #if defined(FEAT_XIM) && defined(FEAT_GUI_GTK)
 		    || im_is_preediting()
 #endif
+#if defined(FEAT_TEXT_PROP)
+		    || popup_no_mapping()
+#endif
 		    )
 	    {
 		// no mapping after modifier has been read