[face] Let hashmap derive invalid key/value types

Works now with the previous two fixes.
diff --git a/src/hb-face.cc b/src/hb-face.cc
index a3df918..b54ec8c 100644
--- a/src/hb-face.cc
+++ b/src/hb-face.cc
@@ -624,7 +624,7 @@
 
 struct hb_face_builder_data_t
 {
-  hb_hashmap_t<hb_tag_t, hb_blob_t*, (unsigned)-1, nullptr> tables;
+  hb_hashmap_t<hb_tag_t, hb_blob_t *> tables;
 };
 
 static int compare_entries (const void* pa, const void* pb)