wtp can send an empty discovery request

FossilOrigin-Name: 440ee8b077901e593d994ef900088b648204f1c8637b35189a5cddd18ec8f08f

src/cw/mlist_replace.c

@@ -0,0 +1,14 @@
+#include "mlist.h"
+
+struct mlistelem * mlist_replace(mlist_t list, void *data)
+{
+	struct mlistelem *e;
+	
+	e = mlist_get(list,data);
+	if (e == NULL)
+		return NULL;
+
+	memcpy(mlistelem_dataptr(e), data,list->data_size);
+	return e;
+
+}