Set errno to EINVAL on missing entry.  It's sort of an odd error code,
but it's consistent with unicode_character_data() and it leaves ENOENT
free in case there is an implementation of the API in the future which
relies on external files.
diff --git a/nametoucs.c b/nametoucs.c
index 12c96dd..4a9a414 100644
--- a/nametoucs.c
+++ b/nametoucs.c
@@ -47,6 +47,7 @@
 
   if ( !ucd->name || strcmp(name, ucd->name) ) {
     unicode_character_put(ucd);
+    errno = EINVAL;
     return NULL;
   }