[OTLayout] Fix collect_glyphs() recursion in ContextFormat3

src/hb-ot-layout-gsubgpos-private.hh

diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index fe4dcbc..7bf3e71 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -1269,7 +1269,7 @@
     const LookupRecord *lookupRecord = &StructAtOffset<LookupRecord> (coverage, coverage[0].static_size * glyphCount);
     struct ContextCollectGlyphsLookupContext lookup_context = {
       {collect_coverage},
-      NULL
+      this
     };
 
     context_collect_glyphs_lookup (c,