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/main.c b/src/main.c
index 33ac89c..5545cc4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4339,7 +4339,7 @@
      *  <lt> sequence is recognised - needed for a real backslash.
      */
     p_cpo = (char_u *)"Bk";
-    str = replace_termcodes((char_u *)str, &ptr, FALSE, TRUE, FALSE);
+    str = replace_termcodes((char_u *)str, &ptr, REPTERM_DO_LT, NULL);
     p_cpo = cpo_save;
 
     if (*ptr != NUL)	/* trailing CTRL-V results in nothing */