[aat] Ignore cross-stream offset of deleted-glyphs

I think it makes sense to accumulate it, but Ned tells me that's
what CoreText does.

src/hb-aat-layout.cc

@@ -232,7 +232,7 @@ hb_aat_layout_zero_width_deleted_glyphs (hb_buffer_t *buffer)
   hb_glyph_position_t *pos = buffer->pos;
   for (unsigned int i = 0; i < count; i++)
     if (unlikely (info[i].codepoint == AAT::DELETED_GLYPH))
-      pos[i].x_advance = pos[i].y_advance = 0;
+      pos[i].x_advance = pos[i].y_advance = pos[i].x_offset = pos[i].y_offset = 0;
 }
 
 static bool