patch 8.1.1759: no mode char for terminal mapping from maparg()

Problem:    No mode char for terminal mapping from maparg().
Solution:   Check for TERMINAL mode. (closes #4735)
diff --git a/src/getchar.c b/src/getchar.c
index e0c8fda..0048ae0 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -4009,6 +4009,8 @@
 	    ga_append(&mapmode, 'n');			/* :nmap */
 	if (mode & OP_PENDING)
 	    ga_append(&mapmode, 'o');			/* :omap */
+	if (mode & TERMINAL)
+	    ga_append(&mapmode, 't');			/* :tmap */
 	if ((mode & (VISUAL + SELECTMODE)) == VISUAL + SELECTMODE)
 	    ga_append(&mapmode, 'v');			/* :vmap */
 	else