[HB] Tweak some constants and fix Coverage
diff --git a/src/hb-ot-layout-gsubgpos-private.h b/src/hb-ot-layout-gsubgpos-private.h
index f9a1f6b..01b7fae 100644
--- a/src/hb-ot-layout-gsubgpos-private.h
+++ b/src/hb-ot-layout-gsubgpos-private.h
@@ -188,6 +188,8 @@
       lookupRecord++;
       lookupCount--;
       i += buffer->in_pos - old_pos;
+      if (HB_UNLIKELY (buffer->in_pos == end))
+	return true;
 
       if (!done)
 	goto not_applied;