Simplify ZWJ-skipping a bit

Towards disabling ZWJ-skipping in certain GPOS contexts.

Part of https://github.com/flutter/flutter/issues/16886

src/hb-ot-layout-gsubgpos.hh

diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 6ff19e2..031b39b 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -344,10 +344,10 @@
       match_glyph_data = nullptr;
       matcher.set_match_func (nullptr, nullptr);
       matcher.set_lookup_props (c->lookup_props);
-      /* Ignore ZWNJ if we are matching GSUB context, or matching GPOS. */
+      /* Ignore ZWNJ if we are matching GPOS, or matching GSUB context and asked to. */
       matcher.set_ignore_zwnj (c->table_index == 1 || (context_match && c->auto_zwnj));
-      /* Ignore ZWJ if we are matching GSUB context, or matching GPOS, or if asked to. */
-      matcher.set_ignore_zwj  (c->table_index == 1 || (context_match || c->auto_zwj));
+      /* Ignore ZWJ if we are matching context, or asked to. */
+      matcher.set_ignore_zwj  (context_match || c->auto_zwj);
       matcher.set_mask (context_match ? -1 : c->lookup_mask);
     }
     inline void set_lookup_props (unsigned int lookup_props)