Revert "Don't process lookups if buffer is in error"

This reverts commit f92bd86cc8.

We don't want to be like cairo, where as soon as there's an error,
nothing works anymore.  So, lets process lookups as long as there's
no new memory needed.  That's also a model that hides fewer bugs.

src/hb-ot-layout.cc

@@ -954,7 +954,7 @@ apply_string (OT::hb_apply_context_t *c,
 {
   hb_buffer_t *buffer = c->buffer;
 
-  if (unlikely (buffer->in_error || !buffer->len || !c->lookup_mask))
+  if (unlikely (!buffer->len || !c->lookup_mask))
     return;
 
   c->set_lookup_props (lookup.get_props ());