patch 8.1.2145: cannot map <C-H> when modifyOtherKeys is enabled

Problem:    Cannot map <C-H> when modifyOtherKeys is enabled.
Solution:   Add the <C-H> mapping twice, both with modifier and as 0x08.  Use
            only the first one when modifyOtherKeys has been detected.
diff --git a/src/usercmd.c b/src/usercmd.c
index c6bf7fe..b48f157 100644
--- a/src/usercmd.c
+++ b/src/usercmd.c
@@ -868,7 +868,7 @@
     char_u	*rep_buf = NULL;
     garray_T	*gap;
 
-    replace_termcodes(rep, &rep_buf, FALSE, FALSE, FALSE);
+    replace_termcodes(rep, &rep_buf, 0, NULL);
     if (rep_buf == NULL)
     {
 	// Can't replace termcodes - try using the string as is