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.

src/getchar.c

@@ -1574,6 +1574,9 @@ vgetc(void)
 	    if (mod_mask
 #if defined(FEAT_XIM) && defined(FEAT_GUI_GTK)
 		    || im_is_preediting()
+#endif
+#if defined(FEAT_TEXT_PROP)
+		    || popup_no_mapping()
 #endif
 		    )
 	    {