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/highlight.c b/src/highlight.c
index 0fdd93a..1333362 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -1417,7 +1417,8 @@
 		 */
 		for (p = arg, off = 0; off < 100 - 6 && *p; )
 		{
-		    len = trans_special(&p, buf + off, FALSE, FALSE);
+		    len = trans_special(&p, buf + off, FALSE, FALSE,
+								   TRUE, NULL);
 		    if (len > 0)	    // recognized special char
 			off += len;
 		    else		    // copy as normal char